Search

PURPOSE We have previously developed and externally validated a prognostic model of overall survival (OS) in men with metastatic, castration-resistant prostate cancer (mCRPC) treated with docetaxel. We sought to externally validate this model in a broader group of men with docetaxel-naïve mCRPC and in specific subgroups (White, Black, Asian patients, different age groups, and specific treatments) and to classify patients into validated two and three prognostic risk groupings on the basis of the model. METHODS Data from 8,083 docetaxel-naïve mCRPC men randomly assigned on seven phase III trials were used to validate the prognostic model of OS. We assessed the predictive performance of the model by computing the time-dependent area under the receiver operating characteristic curve (tAUC) and validated the two-risk (low and high) and three-risk prognostic groups (low, intermediate, and high). RESULTS The tAUC was 0.74 (95% CI, 0.73 to 0.75), and when adjusting for the first-line androgen receptor (AR) inhibitor trial status, the tAUC was 0.75 (95% CI, 0.74 to 0.76). Similar results were observed by the different racial, age, and treatment subgroups. In patients enrolled on first-line AR inhibitor trials, the median OS (months) in the low-, intermediate-, and high-prognostic risk groups were 43.3 (95% CI, 40.7 to 45.8), 27.7 (95% CI, 25.8 to 31.3), and 15.4 (95% CI, 14.0 to 17.9), respectively. Compared with the low-risk prognostic group, the hazard ratios for the high- and intermediate-risk groups were 4.3 (95% CI, 3.6 to 5.1; P < .0001) and 1.9 (95% CI, 1.7 to 2.1; P < .0001). CONCLUSION This prognostic model for OS in docetaxel-naïve men with mCRPC has been validated using data from seven trials and yields similar results overall and across race, age, and different treatment classes. The prognostic risk groups are robust and can be used to identify groups of patients for enrichment designs and for stratification in randomized clinical trials.

18 Background: TRITON3 (NCT02975934) is a randomized, multicenter, open-label, phase 3 study of rucaparib vs physician’s choice (docetaxel [DTX], abiraterone [ABI] or enzalutamide [ENZ]) in patients (pts) with chemotherapy-naïve mCRPC with BRCA1/2 (BRCA) or ATM alterations. It was previously reported that rucaparib significantly improved the primary endpoint of radiographic progression-free survival (rPFS) vs physician’s choice in pts with BRCA or ATM alterations. We report here the interim overall survival (OS) and also report on efficacy of rucaparib compared individually with either DTX or ABI/ENZ. Methods: Pts had disease progression after 1 prior second-generation androgen pathway inhibitor therapy in any setting and were randomized 2:1 to rucaparib 600 mg BID or physician’s choice of DTX, ABI or ENZ. An ordered step-down multiple comparisons procedure was used to control the overall error rate. OS was a key secondary endpoint with rPFS as the primary endpoint tested first in the BRCA subgroup, then the intent-to-treat (ITT) population. Subgroup analyses based on physician’s choice were exploratory. Results: As of August 25, 2022, 302 pts with BRCA and 103 pts with ATM alterations were randomized. OS maturity was 54% in the BRCA subgroup and 59% in the ITT population. rPFS and OS are shown. The most frequent treatment-emergent adverse event (TEAE) in the rucaparib, DTX and ABI/ENZ groups was asthenia/fatigue (61.1%, 67.6% and 57.6%, respectively). The most frequent grade ≥3 TEAE in the rucaparib, DTX and ABI/ENZ groups was anemia (23.7%), neutropenia (14.1%), and hypertension (10.2%), respectively. Conclusions: Rucaparib significantly improved rPFS vs either DTX or ABI/ENZ; safety was consistent with prior reports. Interim OS results suggest a trend towards improvement for rucaparib vs DTX or ABI/ENZ in pts with mCRPC and BRCA alterations. Clinical trial information: NCT02975934 . [Table: see text]

208 Background: In the Phase 3 PRESTO study, intensified androgen deprivation therapy (ADT) with apalutamide (APA) with or without abiraterone acetate plus prednisone (AAP), administered for a finite treatment period of 52 weeks, prolonged prostate-specific antigen progression-free survival (PSA PFS) in pts with high-risk biochemically relapsed prostate cancer (BRPC). We evaluated baseline factors associated with PSA PFS in this study. Methods: PRESTO is a randomized phase 3, open-label trial in pts with BRPC following radical prostatectomy (RP) and PSA doubling time (PSADT) ≤ 9 months (mo), without distant metastases on conventional imaging (NCT03009981). Pts were randomized 1:1:1 to receive a finite 52-week treatment course with ADT, ADT + APA, or ADT + APA + AAP, stratified by PSADT (< 3 vs 3–9 mo), with post-treatment follow-up. Baseline factors associated with PSA PFS including Gleason sum at RP (6-7, 8, ≥ 9) were analyzed in a post hoc fashion. Results: 504 pts were randomized to ADT alone (N = 167), ADT + APA (N = 168) or ADT + APA + AAP (N = 169). Baseline patient characteristics including Gleason sum at diagnosis, serum PSA and PSADT at study entry, time interval from radical prostatectomy, and receipt of prior radiation (none, adjuvant, salvage) were well balanced across the three treatment arms. At the first planned interim analysis, both experimental arms significantly prolonged PSA PFS compared to the control arm (median 24.9 mo for ADT + APA vs 20.3 mo for ADT, HR = 0.52 (95% CI: 0.35–0.77); median 26.0 mo for ADT + APA + AAP vs 20.0 mo for ADT, HR = 0.48 (95% CI: 0.32–0.71)). Across the study cohort, Gleason sum ≥ 9 at diagnosis was associated with shorter PSA PFS (median 21.9 mo for Gleason ≥ 9 vs. 31.1 mo for Gleason 8 vs. 25.2 mo for Gleason 6-7, log-rank p-value = 0.0409). In addition, within each treatment arm, a shorter observed median PSA PFS was detected for patients with Gleason ≥ 9 prostate cancer. Serum PSA and PSADT at study entry, time from prior radical prostatectomy, and prior radiation were not associated with PSA PFS in the overall study cohort or in individual study arms. Conclusions: Gleason sum ≥ 9 prostate cancer at diagnosis was associated with shorter time to PSA progression following subsequent intensified ADT administered for a finite treatment interval in BRPC. Follow-up is ongoing to integrate genomic profiling of primary prostate cancer tissue with these results and validate with longer term endpoints including metastasis-free survival. Clinical trial information: NCT03009981 .

5045 Background: mCRPC is a lethal condition with limited effective treatment options. B7-H3, a transmembrane protein of the B7 checkpoint superfamily is overexpressed in prostate cancer (PC) and is associated with poor prognosis. While several novel approaches target B7-H3 in prostate cancer, lack of knowledge about the molecular features and regulatory mechanisms of B7-H3 expression in mCRPC prevents the optimal design of these interventions. We aimed to characterize B7-H3 in mCRPC with the purpose to reveal the roles of B7-H3 in mCRPC pathogenesis, and stratify the patient population optimal for B7-H3–targeted therapies. Methods: We conducted bioinformatic interrogations at genome-scale on whole-exome and whole-transcriptome sequencing (WES, WTS) data from SU2C/PCF (n = 209, mCRPC), SUWC (n = 101, mCRPC) and GTEx (n = 246, benign prostate tissue). We developed and utilized novel machine learning (ML) algorithms to examine the association of B7-H3 with other key PC pathways. We examined the genetic and epigenetic regulation of B7-H3 by CHIP-seq. We also performed single-cell mRNA sequencing (scRNA-seq) analysis on one patient before and after treatment with the AR inhibitor, enzalutamide. We utilized both Gene Set Enrichment Analysis (GSEA) and our ML approaches to identify enriched signaling pathways in high B7-H3–expressing mCRPC. Results: Expression of B7-H3 was significantly elevated in mCRPC compared to benign prostate tissues, and was distinctive from other B7 family members. High B7-H3 expression was significantly associated with ERG fusions, AR-V7 variant, and increased FOXA1 and androgen receptor (AR) mRNA expression. At gene-level analysis, our ML algorithm suggested that B7-H3 shared similar gene networks as AR and its co-regulators, HOXB13, and FOXA1. CHIP-seq analysis revealed that the distal enhancers of B7-H3 in mCRPC were hyperactive (based on enhanced H3K27Ac marks) relative to primary tumors. Notably, these B7-H3 enhancers were bound by HOXB13, FOXA1 and AR in mCRPC samples. Our scRNA-seq analysis of one patient resistant to enzalutamide showed increased number of B7-H3-expressing cells. Based on integrated GSEA and ML analyses on WTS data, B7-H3 was positively associated with TGF-beta signaling, an enzalutamide resistance pathway. Conclusions: In mCRPC, we found B7-H3 overexpression as compared to other B7 family members. The association of B7-H3-high expression and certain genomic alterations may stratify mCRPC patients for B7-H3–targeted therapy. Further, B7-H3 exhibited regulation by AR, HOXB13 and FOXA1, at the B7-H3 enhancers. The activating epigenetic modification at the distal enhancers represents another potential marker to examine B7-H3 expression in tumors. Altogether, our study indicates that B7-H3 is a critical target in mCRPC patients, including those resistant to enzalutamide.

5053 Background: Recurrent alterations in the WSP have been identified in patients with advanced prostate cancer. Aberrant Wnt signaling has been implicated in disease progression and hormonal resistance in prostate cancer. We utilized a multi-institutional real-world dataset to characterize molecular alterations in the canonical WSP in men with prostate cancer, and correlate that with overall survival (OS). Methods: Prostate cancer patients who underwent tissue-based DNA and RNA sequencing utilizing a commercially available CLIA-certified assay (Caris Life Sciences) were investigated. Next generation sequencing (NGS)/ whole exome (WES) and transcriptome sequencing (WTS) was performed on prostate cancer tissue derived from prostatic and/or metastatic sites. Patients with somatic activating mutations in CTNNB, pathogenic fusions in RSPO2, or inactivating mutations in APC or RNF43 were characterized as having aberrant canonical Wnt signaling (WSP-MT). A subset analysis was conducted in metastatic prostate cancer (mPCa) samples with microsatellite stable (MSS) tumors excluding RNF43 (G569fs*) mutations. Comparative analyses were done using Fisher-Exact or X2 tests, and significance was determined by adjusted p value using Benjamini-Hochberg correction (q < 0.05). OS was obtained from insurance claims data and calculated using Kaplan-Meier estimates. Enriched mRNA transcripts were identified as those with an adjusted p value < 0.001, logFC > 1.5, and (-)log10 FDR > 20. Results: Overall, 21.8% (n = 715/3283) of samples were classified as WSP-MT, of which 297 (41.5%) were from primary tumor samples and 418 (58.5%) were from metastatic sites. WSP-MT were highest in metastases to CNS (54.5%, n = 12/22), liver (43.8%, n = 91/208) and lung (42.3%, n = 91/208). Compared to WSP wild-type, WSP-MT tumors had a greater frequency of dMMR/MSI-H status (18% vs. 2%, q < 0.001). In the subset of mPCa, MSS tumors (WSP-MT excluding RNF43 (G569fs*) mutations, n = 318; WSP wild-type n = 951), WSP-MT were enriched for mutations in SPOP (14.3% vs. 6.9%, q = 0.004). In these tumors, WSP-MT samples were most enriched for mRNA expression of CST1, NKD1, AXIN2, and ZNRF3 (all known canonical WSP activators). OS was inferior in mPCa WSP-MT patients compared to WSP wild-type (HR 0.49, 95% CI 0.37-0.64, p < 0.0001). Relative to WSP wild-type cases, OS was shorter from time of enzalutamide/abiraterone/apalutamide start (HR 0.25, 95% CI 0.15-0.43, p = 0.0001), and from first-line taxane chemotherapy (HR 0.47, 95% CI 0.21-1.02, p = 0.052) in pts with WSP-MT. Conclusions: Canonical WSP alterations are enriched in metastatic tumors, with highest prevalence in visceral (CNS, liver, lung) metastases. Clinical outcomes in WSP-mutant cancers are inferior with both hormonal and chemotherapies, heralding an urgent need to develop novel therapeutic strategies for such patients.

4127 Background: NENs can occur in many locations but have limited precision therapy options. DLL3 is a cell surface protein that is emerging as a promising therapeutic target in NENs including neuroendocrine prostate cancer (NEPC) and small cell lung cancer (SCLC). Our recent study indicated that ̃77% of NEPCs expressed DLL3, with expression in circulating tumor cells being highly concordant with matched biopsies. While there are ongoing clinical trials of drugs targeting DLL3, the repertoire of clinical and genomic features shared across other DLL3-expressing NEN cancers is ill-defined. Methods: We analyzed WES and WTS data from NENs identified across 29 different sites of origin using the Caris Life Sciences platform, excluding SCLC and including neuroendocrine carcinomas and neuroendocrine tumors. We used values above or below median DLL3 expression of all NEN samples to define DDL3-High/Low (H/L). Significance of molecular alterations in DLL3-H vs L was determined using Fisher’s-Exact/Mann Whitney/X2 test with Benjamini-Hochberg correction. Results: DLL3 expression across all 2672 NEN samples was observed in 27 of 29 NENs after excluding SCLC. NENs of anus, prostate, lung, bladder, and bile duct exhibited the greatest median DLL3 expression, whereas adrenal gland, small bowel, and nervous system displayed the lowest. Certain tissues of origin displayed more robust DLL3 expression, with 71% (50/66) of NEPC, 75% (87/122) of lung, and 77.3% (51/66) of bladder being DLL3-H compared to 14.4% (13/90) of adrenal and 7.9% (12/151) of small bowel NENs. DLL3-H NENs were associated with TMB-high status ( > 10 muts/Mb; 12.1% vs 4.5%, OR 2.7, q < 0.001) and more genomic alterations in several driver genes, including tumor suppressors TP53 (51% vs 23%, OR 2.3, q < 0.001) and RB1 (42% vs 10%, OR 4.2, q < 0.001), and oncogenes KRAS (14% vs 5.4%, OR 2.5, q < 0.001), MYC (5.7% vs 0.9%, OR 6.3, q < 0.001) and CCNE1 (5.3% vs 1.3%, OR 4.0, q = 0.001). Conversely, DLL3-L NENs exhibited more alterations in CTNNB1 (2.2% vs 5.2%, OR 0.42, q = 0.04), MEN1 (3.3% vs 11%, OR 0.30, q < 0.001), and BCOR (1.3% vs 4.1%, OR 0.32, q = 0.02). DLL3-H NENs also had significantly more alterations in PIK3CA (6.4% vs 3.0%, OR 2.1, q = 0.04), chromatin remodeling genes KMT2D (6.7% vs 2.6% OR 2.6, q = 0.005) and CREBBP (3.2% vs 0.9%, OR 3.6, q = 0.03), and WNT signaling gene APC (9.7% vs 5.2%, OR 1.9, q = 0.02). Conclusions: We confirmed DLL3 expression in NENs across different tissues of origin, with highest expression in poorly differentiated NENs. DLL3-H expression was associated with genomic features considered “undruggable” based on current precision therapy approaches. Therefore, DLL3-targeted therapies may serve as a promising strategy for NEN patients with functional loss of tumor suppressors TP53 and RB1, as well as increased activity of KRAS, WNT and MYC signaling.

TPS5107 Background: Despite a growing number of treatment options for first line mCRPC, approximately 40% of patients (pts) have radiographic progression within the first year. Androgen receptor (AR) signaling inhibition increases genomic instability with double-strand DNA breaks & co-inhibition of AR & PARP induces synthetic lethality in multiple preclinical models. Homologous recombination repair (HRR) gene aberrations do not appear to be necessary for this synergy as demonstrated in a ph 3 clinical trial of abiraterone & olaparib where this combination improved radiographic progression-free survival (rPFS) in HRR-wild-type pts compared with abiraterone alone. A ph 1b trial has since shown that enzalutamide plus rucaparib has acceptable safety profile & no significant drug-drug interactions (S-DDI). Methods: CASPAR/A031902 (NCT04455750) is a ph 3 study in which 984 pts will be randomized 1:1 to enzalutamide plus rucaparib or placebo. HRR gene aberration is not required for enrollment. All pts will undergo next-generation targeted-exome sequencing from archival tumor tissue (new biopsy only required if no archival tissue available). Treatment will be continued until disease progression & crossover is not allowed. Key eligibility criteria are age ≥ 18 years, ECOG PS 0-2, biopsy-proven prostate adenocarcinoma, progressive (PSA or radiographic) disease per Prostate Cancer Working Group 3 guidelines, measurable or nonmeasurable disease per RECIST 1.1, no prior treatment for mCRPC (prior docetaxel, abiraterone, darolutamide, or apalutamide in non-mCRPC setting is allowed), no significant uncontrolled comorbidity, & no medications with S-DDI with enzalutamide/rucaparib. Hierarchical co-primary endpoints are rPFS & overall survival (OS). The OS analysis will be undertaken as a primary endpoint if the rPFS endpoint is met. For a one-sided logrank test with a type 1 error rate equal to 0.025, the study has 90% power to detect a hazard ratio (HR) of 0.71 in rPFS (median rPFS of 15 & 21 months in control & combination arms, respectively) & 80% power to detect an HR of 0.80 in OS (median OS of 32 & 40 months, respectively). Key secondary endpoints are rPFS & OS in pts with vs without pathogenic BRCA1, BRCA2, or PALB2 alterations; & differences in adverse events & quality of life (QOL) outcomes between the treatment arms. QOL assessments include Functional Assessment of Cancer Therapy–Prostate (FACT-P), Brief Pain Inventory Short Form (BPI-SF) & EQ-5D-5L. A key correlative endpoint is the sensitivity of ctDNA-based testing for alterations in HRR genes. Enrollment to CASPAR began in July 2021 & the study is available for participation to all US-NCTN sites with a projected enrollment of 3 years. Support: U10CA180821, U10CA180882, U24CA196171; U10CA180888. Clinical trial information: NCT04455750.

3150 Background: Histone deacetylase (HDAC) inhibition downregulates HIF-1a, which may be effective in overcoming resistance to VEGF-targeting tyrosine kinase inhibitors. We report the updated survival follow-up for patients treated with abexinostat and pazopanib in a phase Ib trial. Methods: Patients with solid tumor malignancies were enrolled in this phase Ib, open-label trial (NCT01543763) of abexinostat in combination with pazopanib (3+3 design), with a dose expansion restricted to renal cell carcinoma (RCC). Patients received a 1-week run-in period with abexinostat alone, and then combination abexinostat with pazopanib during a 28-day treatment cycle until disease progression, unacceptable toxicity or study withdrawal. Plasma samples from 29 patients were sent for metabolomics analysis. Results: 51 patients were enrolled: N = 36 patients in dose escalation, N = 15 in dose expansion. At the time of last report in 2017, 5 patients remained on study treatment: N = 4 with RCC, and N = 1 with thymic neuroendocrine carcinoma. 4 of these patients have now had disease progression. Median duration of therapy measured 44.9 months (range 39.8-102.2). One patient with metastatic RCC (patient 1) remains on study treatment, after progression on 5 prior lines of systemic therapy. With updated survival follow-up, median OS measured 12.4 months in the dose escalation arm and 27.65 months in the RCC dose expansion cohort. Overall median duration of therapy in all 51 patients measured 5.6 months (range 1-103 months). Progression-free survival among patients with high PBMC HDAC2 expression (> 0.4) remains longer compared to those with low expression (median 6.3 vs. 3.7 months, p = 0.0041). Metabolomics analysis demonstrated a negative correlation between HDAC2 and N6-acetyllysine, suggesting that baseline HDAC2 may impact efficacy of HDAC inhibition. Conclusions: The combination of abexinostat with pazopanib appears promising, with the potential for long-term responses particularly in patients with metastatic RCC. This has led to an ongoing phase III trial examining this combination in RCC. Clinical trial information: NCT01543763. [Table: see text]

3125 Background: Fumarate Hydratase (FH) encodes an essential enzyme in the TCA cycle. Inactivating germline mutations in FH lead to hereditary leiomyomatosis and renal cell cancer syndrome with risk of development of certain cancers. Sporadic FH mutations have been described in different cancers but implications of somatic mutations on cancer outcomes and survival are not well described. Here, we characterize the molecular landscape of FH-mutant cancers. Methods: Tumors analyzed using NGS (NextSeq, 592 genes; NovaSeq, WES), IHC, and WTS (NovaSeq) (Caris Life Sciences, Phoenix, AZ). PD-L1 tested by 22c3, 28-8 (Agilent) and SP-142 (Spring Biosciences) IHC (>1%). MSI tested by FA, IHC, and NGS. TMB measured by totaling somatic mutations per tumor (TMB-h > 10 mutations/MB). Real-world overall survival was extracted from insurance claims data and calculated from first treatment to last contact using K-M survival curves for molecularly defined cohorts. Statistical significance was determined using chi-square and Wilcoxon rank-sum test, adjusted for multiple comparisons (q

e17005 Background: BRAF is a proto-oncogene that is altered in various cancers and is a druggable target. Particularly, the selective BRAF kinase inhibitors Dabrafenib and Vemurafenib are FDA approved for melanoma and thyroid cancer that harbor the activating BRAF V600 hotspot mutations. In pre-clinical studies, activated BRAF promotes tumor cell function across many additional cancer types in which therapeutics have not been considered. We propose that identifying BRAF-activated cancers will guide future pre-clinical investigations and potentially expand the usage of existing BRAF-targeting therapeutics. Methods: We utilized bioinformatics to investigate the molecular profiles of pan-cancer cohorts from two platforms based on distinct sequencing technology. This included a custom curated dataset (whole exome, 6 studies, 39 cancer types, n = 12,019) and GENIE9.1 (targeted gene panel, 62 cancer types, n = 78,619). Studies were included based on genomic modalities (copy number alterations, mutations, gene fusions). We cataloged the frequency and all types of BRAF genomic alterations pan-cancer. We also examined other genomic features, including tumor mutational burden (TMB) and fraction of the genome altered (FGA), and their association with types of BRAF alterations across cancer types. Results: In both platforms, we found that BRAF alterations were observed across over 80% of cancer types. Melanoma, thyroid, and colorectal tumors exhibited the greatest rates of mutations. Regarding gene body rearrangements, we noted endocrine-driven cancers including ovarian and metastatic prostate tumors (mPC) exhibited relative robust rates of amplification. In addition, thyroid carcinoma and mPC harbored recurrent BRAF gene fusion events. In mPC, we found that the BRAF gene fusions often included an N-terminus gene fragment from known androgen-target genes (TMPRSS2 and SND1). These fusion events represented a dysregulated hormone-driven mechanism of BRAF activation. We also found that hotspot missense mutations were cancer-type specific, including K601 hotspots in mPC, G469 hotspots in non-small cell lung cancers, and G466 hotspots in ovarian cancers. Lastly, BRAF-amplified endocrine tumors harbored a 1.5-fold increase in FGA medians, whereas BRAF-mutated lung and colorectal tumors exhibited a 1.6-fold increase in TMB medians. Conclusions: Our molecular analysis revealed that cancers accrued activated BRAF through cancer-type-specific and divergent genomic mechanisms. These molecular features provide genomic evidence to expand the application of BRAF-targeted therapies in additional cancer lineages, including mPC. BRAF mutations were also associated with genomic biomarkers, such as TMB, which may predict response to immune therapies. This suggests that BRAF alterations can be considered as an additional feature to aid therapy selection.

TPS194 Background: Despite a growing number of treatment options for first line mCRPC, approximately 40% of patients (pts) have radiographic progression within the first year. Androgen receptor (AR) signaling inhibition increases genomic instability with double-strand DNA breaks & co-inhibition of AR & PARP induces synthetic lethality in multiple preclinical models. Homologous recombination repair (HRR) gene aberrations do not appear to be necessary for this synergy as demonstrated in a ph 2 clinical trial of abiraterone & olaparib where this combination improved radiographic progression-free survival (rPFS) in HRR-wild-type pts compared with abiraterone alone. A ph 1b trial has since shown that enzalutamide plus rucaparib has acceptable safety profile & no significant drug-drug interactions (S-DDI). Methods: CASPAR/A031902 (NCT04455750) is a ph 3 study in which 984 pts will be randomized 1:1 to enzalutamide plus rucaparib or placebo. HRR gene aberration is not required for enrollment. All pts will undergo next-generation targeted-exome sequencing from archival tumor tissue (new biopsy only required if no archival tissue available). Treatment will be continued until disease progression & crossover is not allowed. Key eligibility criteria are age ≥ 18 years, ECOG PS 0-2, biopsy-proven prostate adenocarcinoma, progressive (PSA or radiographic) disease per Prostate Cancer Working Group 3 guidelines, measurable or nonmeasurable disease per RECIST 1.1, no prior treatment for mCRPC (prior docetaxel, abiraterone, darolutamide, or apalutamide in non-mCRPC setting is allowed), no significant uncontrolled comorbidity, & no medications with S-DDI with enzalutamide/rucaparib. Hierarchical co-primary endpoints are rPFS & overall survival (OS). The OS analysis will be undertaken as a primary endpoint if the rPFS endpoint is met. For a one-sided logrank test with a type 1 error rate equal to 0.025, the study has 90% power to detect a hazard ratio (HR) of 0.71 in rPFS (median rPFS of 15 & 21 months in control & combination arms, respectively) & 80% power to detect an HR of 0.80 in OS (median OS of 32 & 40 months, respectively). Key secondary endpoints are rPFS & OS in pts with vs without pathogenic BRCA1, BRCA2, or PALB2 alterations; & differences in adverse events & quality of life (QOL) outcomes between the treatment arms. QOL assessments include Functional Assessment of Cancer Therapy–Prostate (FACT-P), Brief Pain Inventory Short Form (BPI-SF) & EQ-5D-5L. A key correlative endpoint is the sensitivity of ctDNA-based testing for alterations in HRR genes. Enrollment to CASPAR began in July 2021 & the study is available for participation to all US-NCTN sites with a projected enrollment of 3 years. Support: U10CA180821, U10CA180882, U24CA196171; U10CA180888; Clovis Oncology; http://acknowledgments.alliancefound.org Clinical trial information: NCT04455750.

382 Background: Hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome is caused by inactivating germline mutations in fumarate hydratase ( FH), predisposing individuals to development of certain cancers. Sporadic FH mutations have been described in different types of cancers, including kidney cancers, but the implications of somatic mutations are not well described. Here, we characterize the molecular landscape of kidney tumors with FH mutations. Methods: Tumors were analyzed using next generation sequencing of DNA (NextSeq, 592 genes and NovaSeq, WES) and RNA (NovaSeq). Immune cell fraction was estimated by immune deconvolution (Quantiseq). Significance was determined by chi-square and Wilcoxon rank sum test and adjusted for multiple comparisons (q-value

287 Background: RCC has a distinct pattern of metastatic spread with common sites of metastasis including the lung, bone, and liver. Less common sites include the brain, adrenal gland, and pancreas. While the pattern of metastatic spread has prognostic significance, the biology driving tropism to specific organ sites has not been fully characterized. We utilized a multi-institutional real-world dataset to examine genomic alterations and transcriptional signatures across the spectrum of metastatic sites in patients with RCC. Methods: RCC tissue specimens derived from the kidney and distant metastatic sites were sequenced utilizing a commercially available Clinical Laboratory Improvement Amendments (CLIA)-certified assay by Caris Life Sciences. Whole exome and transcriptome sequencing was performed. Molecular subgroups were defined according to the IMmotion151 metastatic RCC subtypes, with subgroups determined by a weighted average of gene expression levels. Molecular analysis and PD-L1 expression (SP142) were described by metastasis site. Results: 657 RCC samples from 653 patients underwent molecular profiling. The median age was 62 years (range 14-90) and the majority were male (70.6%). The most common histology was clear cell RCC (n = 509, 77.5%), followed by papillary (n = 63, 9.6%), chromophobe (n = 30, 4.6%), medullary (n = 8, 1.2%), collecting duct (n = 6, 0.9%), and mixed (n = 41, 6.2%). Specimen source included the kidney (n = 340, 51.8%), lung (n = 75, 11.4%), bone (n = 45, 6.8%), lymph nodes (n = 34, 5.2%), liver (n = 28, 4.3%), endocrine glands (adrenal, pancreas, and thyroid; n = 23, 3.5%), brain/CNS (n = 16, 2.4%), and other metastatic sites (n = 96, 14.6%). Compared to kidney, several genes were mutated at higher rates for select metastatic sites, including PBRM1 (59.5% bone, 59.1% endocrine, and 45.9% lung vs 33.8% kidney, p< 0.05) and KDM5C (27.8% endocrine, 29.2% lymph nodes, and 35.3% soft tissue vs 9.3% kidney, p< 0.05). When evaluating metastatic specimens versus kidney specimens, bone metastases had a significantly higher proportion of tumors classified as ‘Angio/stromal’ (n = 19, 42.2%; vs n = 52, 15.4%; p< 0.0001), while liver metastases had a higher proportion of the ‘complement/Ω-oxidation’ subgroup (n = 17, 60.7%; vs n = 48, 14.1%; p< 0.0001). PD-L1 expression in metastatic sites (range 6.8%-21.7%, with exception of 0% in GI; p= 0.09 to 0.99) was not significantly different from the kidney (16.6%). Conclusions: In our contemporary real-world analysis, we demonstrate differential patterns of molecular alterations among sites of metastasis in RCC. Our observations elucidate the biology underlying heterogeneous disease outcomes associated with site of metastasis. Application of predictive signatures by site of metastasis may help inform personalized therapy strategies in advanced RCC. Further studies are warranted to validate our findings.

TPS213 Background: Alterations in the cell cycle signaling pathway are common in mCRPC and may contribute to resistance to AR-targeted therapies. Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) have revolutionized the therapeutic landscape in ER+ breast cancer and have demonstrated robust anti-tumor activity in multiple pre-clinical mCRPC models such as enzalutamide-resistant cell lines, including those with the androgen-receptor splice variant 7 (AR-V7). Pre-clinical synergy has also been seen in multiple studies of CDK4/6i and anti-programmed death 1 (PD-1) or PD-ligand-1 (PD-L1). Additionally, loss of function alterations of CDK12, found in 5-7% of mCRPC, may confer vulnerability to anti-PD-L1 agents. Methods: This multi-center study will enroll 54 unselected mCRPC patients (pts), randomized 1:1 to abema (arm A) or abema + atezo (arm B); and 21 pts with known loss of function mutations in CDK12 (arm C) treated with atezo (n = 5) or abema + atezo (n = 16). All pts will undergo on-treatment (6-week) tumor biopsy. Treatment will be continued until disease progression and crossover is prohibited. Key eligibility criteria are age ≥ 18 years, ECOG PS 0-1, biopsy-proven prostate adenocarcinoma, progressive metastatic disease per Prostate Cancer Working Group 3 (PCWG3), progression/intolerance to ≥ 1 novel antiandrogen in hormone-sensitive or CRPC setting, ineligible for docetaxel/cabazitaxel (progression within 12 months of taxane, pt refusal, investigator discretion), no uncontrolled comorbidity or history of pneumonitis/ILD. Arms A & B will use two stage design for co-primary endpoints of progression-free survival at 6 months using PCWG3 (6m-PFS) and objective response rate (ORR). If ≥ 1/12 pts meet either co-primary endpoint, 2nd stage will open to enroll 15 more pts in that arm. Treatment will be deemed to have meaningful clinical activity (MCA) if ≥ 6/27 meet 6m-PFS or ≥ 5/27 have an ORR. This will provide 86% power for 6m-PFS (34% vs. 12%) and 85% power for ORR (30% vs. 10%) at a one-sided α = 0.08. For MCA in arm C, 16 patients treated with abema+atezo will provide 80-85% power for 6m-PFS (34% vs. 12%) at a one-sided α = 0.05 using a one-sample log-rank test. Primary safety endpoint is the incidence of dose-limiting toxicities in pts receiving abema+atezo. Key secondary endpoints are clinical benefit rate (ORR + stable disease), duration of response and overall survival in arms A and B, and safety events in all arms. Primary exploratory endpoint is comparison of tumoral FoxP3+/CD8+ ratio in pts treated with abema vs. abema + atezo. Additional exploratory endpoints will evaluate association between response and genomic alterations identified from tissue or circulating tumor-derived exosomes. Enrollment began in July 2021 and projected enrollment goal is 3 years (NCT04751929). Clinical trial information: NCT04751929.

4 Background: Penile squamous cell carcinoma (SCC) is a rare and aggressive malignancy with few treatments in the advanced setting and little success of immune-checkpoint inhibitions (ICI). Around half of penile SCC cases are linked to HPV infection. We aimed to report the landscape of somatic alterations and ICI-related biomarkers in penile SCC in the Caris Life Sciences dataset and to establish signatures for HPV-dependent and HPV-independent oncogenesis. Methods: Penile SCC tumors were analyzed using next-generation sequencing of DNA (TruSeq, 45 genes; NextSeq, 592 genes and NovaSeq, whole exome sequencing (WES)) and RNA (NovaSeq). PD-L1 expression was tested by IHC using SP142. Microsatellite instability (MSI) was tested by fragment analysis, IHC and NGS. Tumor mutational burden (TMB) was measured by counting all somatic mutations found per tumor (TMB-high: >10 mutations per MB). HPV16/18 status was determined using WES when available. Significance was determined using chi-square and Wilcoxon rank sum test and adjusted for multiple comparisons (q-value 1%), 10.7% had high TMB, and 1.1% had dMMR/MSI-H. Of the 108 tumors, 29 had HPV status tested by WES (HPV16/18+, n=13 and HPV16/18-, n=16). KMT2C mutations (33% vs 0%) and FGF3 amplifications (30.8% vs 0%) were specific to HPV16/18+ tumors, while CDKN2A mutations (37.5% vs 0%) were exclusive to HPV16/18- tumors. HPV16/18+ tumors also had a trend towards decreased TP53 (7.7% vs 63%) and TERT promoter (25% vs 77%) alterations (Table). TMB-high were exclusively found in the HPV16/18+ group (30.8% vs 0%), while PD-L1 and dMMR/MSI-H status were comparable between the two groups. Conclusions: To our knowledge, our comprehensive NGS study of penile SCC somatic alterations is the largest to date. HPV16/18+ vs HPV16/18- penile SCC were molecularly distinct tumors, consistent with previous reports. Our finding that TMB-high was exclusive to patients with HPV16/18+ tumors requires confirmation in larger datasets and could be used for better patient stratification in ICI clinical trials.[Table: see text]

5063 Background: ATM mutations, one of a family of DNA repair defects prevalent in prostate cancer, have been included in a list of actionable mutations for PARP inhibitor (PARPi) therapeutic trials. Despite preclinical evidence, PARPi have shown minimal clinical activity in ATM mutant prostate cancer (ATMmPCa). The present analysis explores co-occurring genomic alterations that may drive outcomes of metastatic PCa (mPCa) patients with tumors harboring ATM mutations and provide clues for understanding therapy resistance and potential targets. Methods: This study included molecular profiling analysis of 1375 cases of mPCa. Tumors were analyzed using next-generation sequencing (NGS), whole transcriptome sequencing (WTS), and immunohistochemistry (IHC) (Caris Life Sciences, Phoenix, AZ). dMMR/MSI-H status was determined by IHC, NGS, and fragment analysis and tumor mutational burden (TMB) was calculated based on somatic nonsynonymous missense mutations. We performed differential gene expression analysis of HR-associated transcripts such as ATR, PARP1-3, RAD50, RAD51A/B/C/D and RAD54. Significance was determined using the ꭓ2 test and Benjamini-Hochberg method. Results: Fifty-nine (4.2%) cases harbored pathogenic ATM mutations, 84 (6.2%) harbored BRCA2 mutations. 1018 tumors (74%) were deemed homologous recombination proficient (HRP) and 155 tumors (11.3%) were HR Deficient (HRD); harboring one or more mutation in HR-related genes excluding ATM and BRCA2. The mutation rate of TP53 was significantly lower in ATMmPCa (12.0%) compared to BRCA2mPCa (35%), HRD (35%) and HRP (46.6%) tumors. ATMmPCa showed higher rates of SMAD2 (3.7%/1%) and FLCN (5.2%/0.3%) alterations compared to HRP cases. PARP1 and RAD51D gene expression was reduced in ATMmPCa compared to HRP (p < 0.05) and BRCA2mPCa ( p < 0.05) tumors, respectively. No differences in gene expression levels were detected for ATR, PARP2, PARP3, RAD50, and RAD54. Chromosomal segments demonstrating differential CNA in ATMmPCa vs HRP, HRD, or BRCA2mPCa included FGF19, FGF4, PTPN11, ALDH2, DAXX, BCL7A, CCND1, BMPR1A and MEF2B (Q-value < 0.05 determined by ꭓ2). The most common CNA in ATMmPCa was CCND1, present in approximately 13% (7/55) of cases. Compared to BRCA2mPCa and HRD cases, ATMmPCa cases are less likely to display markers of immunotherapy response such as dMMR/MSI-H or TMB ≥10 mutations/MB. Conclusions: ATMmPCa demonstrated several differences in co-occurring alterations compared to BRCA2mPCa, HRD and HRP mPCa. ATMmPCa tumors were less likely to harbor alterations in TP53 compared to BRCA2, HRD or HRP tumors. CNA in ATMmPCa occurred in 9 genes across distinct mPCa molecular subtypes and were enriched for those associated with the 11q13 amplicon harboring Cyclin D1. The FGF and PTPN11 related pathways are potentially targetable pathways in ATMmPC and may merit further study.

25 Background: Comprehensive genomic profiling (CGP) by next-generation sequencing (NGS) of circulating tumor DNA (ctDNA) from plasma provides a minimally invasive method to identify targetable genomic alterations (GAs) and resistance mechanisms in patients with metastatic castration-resistant prostate cancer (mCRPC). The circulating tumor fraction in patients with mCRPC and the clinical validity of GAs detected in plasma remain unknown. We evaluated the landscape of GAs using ctDNA-based CGP and assessed concordance with tissue-based CGP. Methods: Plasma from 3,334 patients with advanced prostate cancer (including 1,674 mCRPC screening samples from the TRITON2/3 trials and 1,660 samples from routine clinical CGP) was analyzed using hybrid-capture-based gene panel NGS assays. Results were compared with CGP of 2,006 metastatic prostate cancer tissue biopsies. Concordance was evaluated in 837 patients with both tissue (archival or contemporaneous) and plasma NGS results. Results: 3,127 patients [94%] had detectable ctDNA. BRCA1/2 were mutated in 295 patients [8.8%]. In concordance analysis, 72/837 [8.6%] patients had BRCA1/2 mutations detected in tissue, 67 [93%] of whom were also identified by ctDNA, and 20 patients were identified using ctDNA but not tissue [23% of all patients identified using ctDNA]. ctDNA detected subclonal BRCA1/2 reversions in 10 of 1,660 [0.6%] routine clinical CGP samples. AR alterations, including amplifications and hotspot mutations, which were detected in 940/2,213 patients [42%]. Rare AR compound mutations, rearrangements, and novel in-frame deletions were identified. Altered pathways included PI3K/AKT/mTOR [14%], WNT/β-catenin [17%], and RAS/RAF/MEK [5%]. Microsatellite instability was detected in 31/2,213 patients [1.4%]. Conclusions: In the largest study of mCRPC plasma samples conducted to date, CGP of ctDNA recapitulated the genomic landscape detected in tissue biopsies, with a high level of agreement in detection of BRCA1/2 alterations. It also identified patients who may have gained somatic BRCA1/2 alterations since archival tissue was collected. ctDNA detected more acquired resistance GAs than tissue, including novel AR-activating variants. The large percentage of patients with rich genomic signal from ctDNA, and the sensitive, specific detection of BRCA1/2 alterations position liquid biopsy as a compelling clinical complement to tissue CGP for patients with mCRPC.

80 Background: The poly(ADP-ribose) polymerase (PARP) inhibitor rucaparib was granted accelerated approval by the US Food and Drug Administration for patients with BRCA+ mCRPC based on results from the phase 2 TRITON2 study (NCT02952534). The TP53 tumor suppressor gene is among the most frequently mutated genes in human cancers, including mCRPC, and alterations in TP53, PTEN, and RB1 are associated with poor prognosis in patients with prostate cancer and other tumor types. We present data on co-occurring alterations in patients with BRCA+ mCRPC treated with rucaparib in TRITON2. Methods: Patients had progressed on 1–2 lines of androgen receptor-directed therapy and 1 taxane-based chemotherapy and were treated with rucaparib 600 mg BID. Tissue and/or cell-free DNA extracted from plasma samples were profiled comprehensively for genomic alterations using Foundation Medicine, Inc., next-generation sequencing assays. Objective response rate (ORR) was assessed per modified Response Evaluation Criteria in Solid Tumors and Prostate Cancer Working Group 3 criteria by independent radiologic review of patients with measurable disease. Prostate-specific antigen (PSA) response rate (≥50% decrease from baseline) was assessed in all patients. Results: Tissue and/or plasma samples were available for 114/115 patients with BRCA+ mCRPC (visit cutoff date: Dec. 23, 2019). Among patients with BRCA+ mCRPC who had samples available for comprehensive genomic profiling, 36.8% (42/114) had a co-occurring alteration in TP53. Deleterious alterations in PTEN were observed in 34.2% (39/114) of patients, 44% (17/39) of which were homozygous deletions of PTEN. RB1 loss was observed in 12.3% (14/114) of patients and was seen more frequently in patients with measurable disease (18.0%, 11/61) than in patients with non-measurable disease (5.7%, 3/53). Although patients with and without TP53 mutations had generally similar baseline demographics and disease characteristics, visceral disease was more prevalent in patients with TP53 mutations (54.8%; 23/42) than in those without them (29.2%; 21/72). Similar ORR and PSA response rates were seen in patients with BRCA+ mCRPC with or without TP53 mutation, with a non-significant trend towards lower response rates in patients with co-occurring TP53 alterations. Conclusions: Results from TRITON2 showed antitumor activity for rucaparib in patients with BRCA+ mCRPC associated with or without co-occurring alterations in TP53. Demographics and additional efficacy analyses in genomic subgroups with co-occurring alterations in TP53, PTEN, and RB1 will be reported. Clinical trial information: NCT02952534. [Table: see text]

TPS181 Background: Treatment with novel antiandrogens (NAA) and androgen deprivation therapy prolongs life in men with mCRPC but approximately 40% patients (pts) have radiographic progression within the first year. Inhibition of androgen receptor signaling results in increased double-strand DNA breaks and genomic instability. NAA+PARP inhibitor (PARPi) combinations have shown induction of synthetic lethality by this mechanism in multiple preclinical studies. Homologous recombination repair (HRR) gene aberrations do not appear to be necessary for this synergy and an NAA+PARPi combination has shown improved radiographic progression-free survival (rPFS) in HRR-wild-type pts compared with NAA alone. Methods: CASPAR (A031902) is a randomized phase 3 study in which 984 pts will be randomized on a 1:1 basis to ENZ plus RUCA/PBO. A PK substudy will precede the phase 3 portion and enroll 6-18 pts to various doses of ENZ plus RUCA to establish safety and evaluate any clinically-significant drug-drug interactions (S-DDI). Treatment will be continued until disease progression and cross-over is not allowed. Co-primary endpoints are rPFS and overall survival (OS). The OS analysis will be undertaken as a primary endpoint if the rPFS endpoint is met. For a one-sided logrank test with a type 1 error rate equal to 0.025, the study has 90% power to detect a hazard ratio (HR) of 0.71 in rPFS (median rPFS of 15 and 21 months in control and combination arms, respectively), and 80% power to detect an HR of 0.80 in OS (median OS of 32 and 40 months, respectively). Key secondary endpoints are rPFS and OS in pts with vs without pathogenic BRCA1, BRCA2, or PALB2 mutations; and differences in adverse events and quality of life (QOL) outcomes between the treatment arms. QOL assessments include Functional Assessment of Cancer Therapy–Prostate (FACT-P), Brief Pain Inventory Short Form (BPI-SF), and EQ-5D-5L. A key correlative endpoint is the concordance between tissue and plasma ctDNA-based HRR testing. Key eligibility criteria are age ≥ 18 years, ECOG PS 0-2, biopsy-proven prostate adenocarcinoma, progressive (PSA or radiographic) disease per Prostate Cancer Working Group 3 guidelines, measurable or non-measurable disease per RECIST 1.1, no prior treatment for mCRPC (prior abiraterone, darolutamide, or apalutamide in non-mCRPC setting is allowed), no significant uncontrolled comorbidity, and no medications with S-DDI with ENZ/RUCA. HRR gene aberration is not required for enrollment. All pts will undergo next-generation targeted-exome sequencing from archival tumor tissue (new biopsy only required if no archival tissue available). CASPAR is available for participation to all US-NCTN sites starting in October 2020 with a projected enrollment of 3 years. Support: U10CA180821, U10CA180882; acknowledgments.alliancefound.org. Clinical trial information: NCT04455750.

79 Background: Rucaparib, a poly(ADP-ribose) polymerase inhibitor (PARPi), is approved in the US as monotherapy for BRCA1/2 mutated mCRPC that has been treated with androgen receptor (AR)-directed therapy and a taxane. In previous studies, synthetic lethality was observed with a combination of AR-directed therapy (eg, enzalutamide) and a PARPi, independent of DNA-damage repair gene defects. The potential for drug-drug interaction between rucaparib and enzalutamide was recognized as enzalutamide is a strong clinical inducer of CYP3A4, a mediator of the formation of rucaparib metabolite M324. RAMP (NCT04179396) is investigating the combination of rucaparib and enzalutamide in unselected pts with mCRPC to assess PK and safety and inform subsequent studies. Methods: Eligible pts had 0–2 lines of AR-directed therapy and ≤2 lines of chemotherapy for mCRPC. Prior PARPi treatment was not allowed. A 1-week run-in of rucaparib monotherapy (600 mg BID) was followed by rucaparib (600 mg BID) + enzalutamide (160 mg QD) in continuous 28-day cycles. Trough PK was evaluated for rucaparib and enzalutamide and their metabolites (M324 and N-desmethyl enzalutamide). Dose-limiting toxicities (DLTs) were assessed during the first 2 cycles. Primary endpoints were PK and safety for the combination. Secondary endpoints were change from baseline in prostate-specific antigen (PSA) levels and objective response rate (per modified RECIST/PCWG3). Results: As of Oct 1, 2020, 8 pts had received treatment; 7 were evaluable for PK and 6 for DLTs. The median age was 68.5 years, and 6/8 (75%) pts had ≥2 prior mCRPC therapies. Rucaparib and M324 reached apparent steady-state PK at the end of the run-in period. Concomitant treatment with enzalutamide had no significant effect on the PK of either rucaparib or M324. The PK of enzalutamide and N-desmethyl enzalutamide in the combination were also consistent with monotherapy enzalutamide PK data. No DLTs were reported. The most common grade ≥3 TEAEs among all 8 pts were anemia (n = 5) and fatigue (n = 4). Seven of 8 (87.5%) pts required a dose modification (treatment interruption or dose reduction). Four of 8 (50%) pts had a confirmed PSA response (reduction ≥50% from baseline); 1/1 (100%) pt with measurable disease achieved a confirmed complete radiographic response. At the time of data cutoff, 1/8 (12.5%) pts was on study for > 6 cycles. Conclusions: A combination of enzalutamide and rucaparib was not associated with a clinically significant effect on PK profiles of either drug. No DLTs were observed. The overall safety profile of rucaparib 600 mg BID + enzalutamide 160 mg QD was consistent with that observed in monotherapy. These PK, safety, and early efficacy data support further studies of rucaparib and enzalutamide at the recommended combination dose, including in the phase 3 CASPAR study in pts with mCRPC (NCT04455750). Clinical trial information: NCT04179396.

465 Background: UTUC is a rare genitourinary malignancy and a number of studies, limited by small sample sizes, have attempted to characterize its mutational landscape. Because immunotherapy is commonly used for this disease type, we evaluated the prevalence of microsatellite instability and characterized the mutational landscapes of UTUC in a large contemporary patient cohort. Methods: UTUC tumor samples were analyzed using next generation sequencing (NGS) (NextSeq, 592 gene panel) or whole exome sequencing (WES) (NovaSeq) (Caris Life Sciences, Phoenix, AZ). Mismatch repair status (deficient [dMMR] or proficient [pMMR]) and microsatellite instability status (MSI-high or stable [MSS]) were detected by immunohistochemistry (IHC), fragment analysis, and NGS. Tumor mutational burden (TMB) was measured by counting all somatic mutations found per tumor (high cutoff ≥ 10 mutations per MB). PD-L1 expression was tested by IHC using PD-L1 antibody clones 22c3 (Agilent; positive cutoff CPS ≥ 10) and SP142 (Ventana; positive cutoff ≥ 5% IC). Pathogenic fusion events were detected using whole transcriptome sequencing (NovaSeq). Statistical significance was determined using the Chi-square test and adjusted for multiple comparison. Results: 538 patients with included – median (range) age 71.5 (30-89) years and 37.5% female/62.5% male. Prevalence of dMMR/MSI-H was 3.9% (21/538) and TMB-high was 22.7% (96/423). Significant molecular differences were not detected in primary vs metastatic disease or in male vs female cases. dMMR/MSI-H tumors had higher frequency of TMB-high compared to MSS tumors (100% vs. 19%, p = 0.00003). dMMR/MSI-H tumors also had a higher frequency than MSS tumors for mutations in genes involved in chromatin remodeling (ASXL 82.4%, CREBBP 60%, SMARCA4 40%, KMT2D 95%, ARIDIA 100%, KMT2A 20%, KMT2C 35.3%, NSD1 20%), DNA-damage repair (FANCG 10%, ATM 45%, ATRX 40%) and other biological pathways (RNF43 10%, PTCH1 21.4%, ERBB3 30%, CDKN2A 25%, TSC2 15%, FLNC 15%, HNF1A 20%, CIC 15%, DNMT3A 17.6%); all adjusted p < 0.05. Pathogenic fusions were detected in 3.8% (17/443) cases, with FGFR3 fusion being the most common, occurring in 2.7% (12/443) cases. PD-L1 positivity was identified in 33.2% (133/400) cases tested by 22c3 antibody and 28.4% (89/313) cases tested by SP142 antibody. No difference was seen in PD-L1 positivity between MSI-H/dMMR vs. MSS tumors. Conclusions: In the largest analysis to date, we found a 3.9% prevalence of dMMR/MSI-high rate in UTUC. All dMMR/MSI-H tumors displayed TMB-high. PD-L1 positivity was comparable between dMMR/MSI-H and MSS tumors. dMMR/MSI-H tumors had a significantly higher rate of mutations in genes involved in chromatin remodeling and DDR biological pathways. These results could inform design of targeted therapy trials in UTUC.

343 Background: With the emergence of multiple active treatment options in RCC, predictive biomarkers for optimal treatment selection are lacking. Gene expression data from IMmotion151 and Javelin Renal 101 clinical trials generated anti-angiogenic and immune signatures that warrant further validation. We aimed to describe the genomic and gene expression profiles in a multi-institutional database of patients with ccRCC, and its association with other biomarkers of interest. Methods: Whole transcriptome sequencing was performed for ccRCC patient samples submitted to a commercial CLIA-certified laboratory (Caris Life Sciences, Phoenix, AZ) from February 2019 to September 2020. Tumor GEP and hierarchical clustering based on the validated 66-gene signature (D’Costa et al, 2020) were used to identify patient subgroups. Samples from both primary tumors and metastatic sites were included. Results: A total of 316 patients with ccRCC, median age 62 (range 32-90), 71.8% men, were included. Tissue samples were obtained from primary tumor (46.5%), lung (12.3%), bone (9.5%), liver (4.7%) and other metastatic sites (27%). Gene expression analysis identified angiogenic, mixed and T-effector subgroups in 24.1%, 51.3% and 24.7%, respectively. Patients with angiogenic subgroup tumors compared to those with T-effector subgroup tumors were more likely to be older (63 versus 60 years, p=0.035), female (40.8% versus 16.7%, p=0.0009) and more frequently found in pancreatic/small bowel metastases (75% versus 12.5%, p=0.0103). Biomarkers of potential response to immunotherapy such as PD-L1 (p=0.0021), TMB (not significant), and dMMR/MSI-H status (not significant) were more frequent in the T-effector subgroup. PBRM1 mutations were more common in the angiogenic subgroup (62.0% vs 37.5%, p=0.0034) while BAP1 mutations were more common in the T-effector subgroup (18.6% versus 3.0%, p= 0.0035). Immune cell population abundance (e.g. NK cells, monocytes) and immune checkpoint gene expression (TIM-3, PD-L1, PD-L2, CTLA4) were also increased in the T-effector subgroup. Conclusions: Our hierarchical clustering results based on the 66-gene expression signature were concordant with results from prior studies. Patient subgroups identified by evaluation of angiogenic and T-effector signature scores exhibit significantly different mutations and immune profiles. These findings require prospective validation in future biomarker-selected clinical trials.

Purpose Evolving treatments, disease phenotypes, and biology, together with a changing drug development environment, have created the need to revise castration-resistant prostate cancer (CRPC) clinical trial recommendations to succeed those from prior Prostate Cancer Clinical Trials Working Groups. Methods An international expert committee of prostate cancer clinical investigators (the Prostate Cancer Clinical Trials Working Group 3 [PCWG3]) was reconvened and expanded and met in 2012-2015 to formulate updated criteria on the basis of emerging trial data and validation studies of the Prostate Cancer Clinical Trials Working Group 2 recommendations. Results PCWG3 recommends that baseline patient assessment include tumor histology, detailed records of prior systemic treatments and responses, and a detailed reporting of disease subtypes based on an anatomic pattern of metastatic spread. New recommendations for trial outcome measures include the time to event end point of symptomatic skeletal events, as well as time to first metastasis and time to progression for trials in the nonmetastatic CRPC state. PCWG3 introduces the concept of no longer clinically benefiting to underscore the distinction between first evidence of progression and the clinical need to terminate or change treatment, and the importance of documenting progression in existing lesions as distinct from the development of new lesions. Serial biologic profiling using tumor samples from biopsies, blood-based diagnostics, and/or imaging is also recommended to gain insight into mechanisms of resistance and to identify predictive biomarkers of sensitivity for use in prospective trials. Conclusion PCWG3 moves drug development closer to unmet needs in clinical practice by focusing on disease manifestations most likely to affect prognosis adversely for therapeutics tested in both nonmetastatic and metastatic CRPC populations. Consultation with regulatory authorities is recommended if a trial is intended to seek support for drug approval.

e19138 Background: mCSPC is clinically complex. Although consensus on treatments are evolving, ADT remains the backbone of therapy. This study assessed the proportion of mCSPC patients treated with ADT only or remaining untreated and their HRU during the mCSPC period in the US. Methods: The Optum Clinformatics Extended DataMart was used to identify men with ≥2 claims for prostate cancer (PC), ≥1 claim for metastasis, ≥1 castration sensitivity (CS) indicator (CS diagnosis code [dx]; castration and no prostate-specific antigen [PSA] rise; or hormone/castration naive for ≥18 months [mo] before index [date of 1st metastasis dx on or after 1st PC dx and between 2015-2018]). Patients were excluded if they had a pre-index castration-resistance (CR) indicator (CR dx; castration within ≥90 days pre-index or with PSA rise; or a claim for a drug solely recommended for metastatic CRPC). mCSPC period (F/U) was defined as time from index until CR (i.e., any post-index CR indicator or initiation of abiraterone acetate or docetaxel ≥12 mo after post-index ADT initiation or ≥12 mo post-index for those with no ADT) or end of data. The proportion of patients receiving ADT only or no mCSPC treatment during F/U was reported. Per-patient-per-year (PPPY) all-cause HRU were evaluated during baseline (12 mo pre-index) and F/U. Descriptive statistics were used: n (%) for binary and mean [SD] for continuous variables. Results: A total of 2,825 mCSPC patients were identified (age: 75 [9] years). Of these, 2,181 (77%) received ADT only or no treatment in a F/U of 10.9 [9.0] mo. Among them, there were more patients with ≥1 inpatient (IP) stay or ≥1 emergency room (ER) visit (F/U vs. baseline; IP: 50% vs. 20%; ER: 57% vs. 44%), and patients had more IP stays and ER visits (IP: 2.0 [4.0] vs. 0.3 [0.7] stays; ER: 3.2 [7.1] vs. 1.1 [2.2] visits) and more IP days (27 [61] vs. 3 [11] days) PPPY in F/U vs. baseline. Trends were similar among patients receiving ADT only (N=1,252 [44%]; F/U of 12.6 [9.0] mo; Table). Conclusions: The majority of mCSPC patients were treated with ADT only or remained untreated and incurred substantial HRU. These findings suggest that improvements in therapy and prompt treatment initiation in men with mCSPC are needed to improve outcomes. [Table: see text]

e19131 Background: Given recent advances in treatment options for mCSPC, this study assessed US real-world treatment patterns of mCSPC patients over time. Methods: The Optum Clinformatics Extended DataMart was used to identify men with ≥2 claims for PC, ≥1 claim for metastasis, ≥1 castration sensitivity (CS) indicator (CS diagnosis code [dx]; castration and no prostate-specific antigen [PSA] rise; or hormone/castration naive for ≥18 months [mo] before metastasis). Index (idx) date was the 1st metastasis dx date on or after 1st PC dx and from 2015-2018. Patients were excluded if they had a pre-idx castration-resistance (CR) indicator (CR dx; castration within ≥90 days pre-idx or with PSA rise; or a claim for a drug solely recommended for metastatic CRPC). mCSPC period (F/U) was defined as time from idx until CR (i.e., any post-idx CR indicator or initiation of abiraterone acetate [ABI] or docetaxel [DOC] ≥12 mo after post-idx androgen deprivation therapy [ADT] initiation or ≥12 mo post-idx for those with no ADT) or end of data. mCSPC treatment patterns in F/U were assessed overall and in patients with idx years (yrs) in 2015-2016 and in 2017-2018, separately. Descriptive statistics were used: n (%) for binary and mean [SD] for continuous variables. Results: In the 2,825 mCSPC patients identified (age: 75 [9] yrs; F/U: 10.9 [9.0] mo), 43% were in the 2015/16 cohort (age: 75 [9] yrs; F/U: 15.8 [10.2] mo); and 57% were in the 2017/18 cohort (age: 75 [9] yrs; F/U: 7.2 [4.7] mo). The most common first-line (1L) mCSPC therapy was ADT only (Table), but patients in the 2017/18 cohort had fewer ADT only as 1L (43% vs. 52%) and more 1L ABI (10% vs. 4%) compared to the 2015/16 cohort. About 4% (2015/16: 5%; 2017/18: 3%) of patients received second-line (2L) mCSPC therapies, with ABI (74%) and DOC (25%) as the main 2L therapies observed. In patients receiving 2L mCSPC therapies, the 2017/18 cohort had more 2L ABI (81% vs. 68%) and fewer 2L DOC (19% vs. 30%) compared to the 2015/16 cohort. Conclusions: A large proportion of men with mCSPC were untreated/deferred treatment or were treated with ADT only, highlighting unmet needs in this patient group. As additional therapies for mCSPC become available, this trend is expected to improve, as supported by more recent treatment patterns. [Table: see text]

5031 Background: The phase 2 TRITON2 study (NCT02952534) is evaluating the PARP inhibitor rucaparib in patients with mCRPC who have a deleterious germline or somatic alteration in BRCA ( BRCA1 or BRCA2) or 1 of 13 other DNA damage repair genes. Here we present analyses of tumor genomics and baseline clinical characteristics in mCRPC patients with a deleterious alteration in BRCA. Methods: Plasma (baseline) and tissue (archival or baseline) samples from patients with a deleterious alteration in BRCA were analyzed using Foundation Medicine next-generation sequencing assays. The alterations and zygosity of the alterations that were detected, as well as the somatic/germline status from Color Genomics testing, were summarized. Associations between genomic alterations, DNA yield, allele frequency, and baseline clinical characteristics were investigated. Results: Results are shown in the Table for a cohort of 40 BRCA2 and 5 BRCA1 patients enrolled in TRITON2 (Abida W et al. Presented at ESMO 2018. Abst 793PD). A biallelic alteration was observed in 21 of the 22 BRCA2 patients (95%) for whom alteration zygosity could be determined. Among the 5 BRCA1 patients, 1 alteration was monoallelic and 4 were of unknown zygosity. Co-occurring alterations in cancer-related or DNA damage repair genes were observed in many patients with BRCA alterations. At baseline, cell-free DNA (cfDNA) yield correlated positively with the sum of target lesions (STL; P= 0.04), but not with prostate-specific antigen (PSA) levels ( P= 0.86). No correlation was observed between allele frequency of the BRCA alteration baseline STL ( P= 0.68) or PSA levels ( P= 0.97). Conclusions: Patients with a BRCA mutation enrolled in TRITON2 demonstrate a profile of genomic alterations consistent with that of prior studies of patients with mCRPC. Plasma cfDNA profiling showed a correlation between baseline cfDNA yield and measurable tumor burden, but not baseline PSA. Clinical trial information: NCT02952534. [Table: see text]

e16579 Background: PM’s in mCRPC accurately predict survival, but little is known about their association with QOL. We hypothesize that pre-treatment QOL is inversely correlated with PM derived scores. Our study explored associations between baseline Halabi PM derived risk score (including metastatic site, opioid use, ECOG performance status (ECOG PS), Alk phos, albumin, hemoglobin, LDH, and PSA) and multiple QOL domains at treatment initiation with docetaxel and prednisone (DP). Methods: The DP arm of MAINSAIL, a multicenter, randomized Phase 3 study of DP +/- lenalidomide in mCRPC, was analyzed via ProjectDataSphere. Halabi PM score was computed as continuous with higher score reflecting worse survival and classified as low- ( < 140 points), intermediate- (140-194.96) or high-risk groups ( > 194.96 points). QOL tests included FACT-P (higher score = better QOL), BPI-SF Severity score (BPI-SFSS; higher score = higher pain severity); and BPI-SF Interference score (BPI-SFIS, higher score = worse pain). General linear regression model was used to calculate beta estimates and 95% confidence intervals. Results: The sample included 526 mCPRC pts (median 68 years, White: 91.9%, Black: 5.3%, median PSA 75.95 ng/ml). Median [range] for FACT-P, BPI-SFSS and BPI-SFIS were 111 [0-152], 1.8 [0-9.3], and 1.4 [0-10], respectively. PM score was correlated with BPI-SFIS and BPI-SFSS and inversely correlated with FACT-P with correlation of 0.36, 0.31 and -0.33, respectively (all p < 0.0001). For each unit increase in the PM score, BPI-SFIS increased by 2.1 points), BPI-SFSS increased by 1.5 points, and FACT-P decreased by 16.4 points. Using the three-risk groups, pts in the intermediate and high-risk groups had worse FACT-P QOL and higher BPI-SFIS and BPI-SFSS than pts in the low-risk group. In multivariate analysis, factors negatively impacting FACT-P QOL, BPI-SFSS and BPI-SFIS were higher ECOG PS, visceral metastases and opioid use. Declining hemoglobin levels were associated with increased BPI-SFSS and BPS-SFIS. Conclusions: Higher PM scores are associated with a lower baseline QOL overall, higher pain and higher pain interference. These results should be validated prospectively.

5008 Background: Androgen receptor (AR) signaling is an important growth mechanism in mCRPC, providing the rationale for treatment with AR axis inhibitors such as ENZ and AAP. Targeting AR with anti-androgens such as ENZ can result in compensatory autocrine and paracrine androgenic stimulation. Therefore, using ENZ with the androgen biosynthesis inhibitor AAP to dampen these resistance mechanisms could improve clinical outcomes relative to ENZ alone. Methods: Men with progressive mCRPC by Prostate Cancer Working Group 2 criteria were eligible. Prior treatment with taxanes for mCRPC and any prior treatment with ENZ or AAP was exclusionary. Patients (pts) were randomized 1:1 to ENZ or ENZ/AAP at standard FDA-approved doses. Randomization was stratified by prior chemotherapy and Halabi prognostic three risk groups. Castrating therapy was maintained. The primary endpoint was overall survival (OS) defined as the date of randomization from date of death or last follow-up. The log-rank test had 90% power to detect a hazard ratio for OS of 0.77 with a one-sided type I error rate of 0.025. Secondary endpoints included radiographic progression free survival (rPFS) and on-treatment PSA declines. Exploratory endpoints included imaging changes, and changes in serum biomarkers such as androgens, angiokines, and circulating microRNA and RNA. The primary analysis was based on the stratified log-rank test adjusting on the stratification factors. Results: Between January 2014 and August 2016, 1311 men were randomized: 657 to ENZ and 654 to ENZ/AAP. Groups were well balanced between arms, including stratification variables. 15.6% of pts were high risk, 35.3% intermediate, and 48.1% low. Median OS was 33.6 mo (95% CI 30.5-36.4) and 32.7 mo (29.9-35.4) respectively, two-sided p = 0.53. Fifty percent PSA decline rate was 80% vs. 76.5%. Grade 3-5 adverse events (AE) (all attributions) were 55.6% and 68.8% respectively. Treatment discontinuation due to AEs occurred in 5% and 12%, pt withdrawal in 5% and 13%, and progression or death in 57% and 48% of pts respectively. Conclusions: Addition of abiraterone acetate to enzalutamide did not prolong survival in men with mCRPC. The combination resulted in more AEs than enzalutamide alone. Support: U10CA180821, U10CA180882, U24CA196171; https://acknowledgments.alliancefound.org . Clinical trial information: NCT01949337.

204 Background: Androgen deprivation therapy (ADT) is associated with numerous metabolic toxicities that are potentially modifiable. We sought to evaluate the impact of participation in a multidisciplinary clinic (MDC) designed to provide individualized lifestyle modification and management of ADT-related side effects. Methods: This phase II study recruited men with prostate cancer who had started ADT < 6 months prior to enrollment, and in whom ADT was planned for at least 12 months following enrollment. Patients were randomized in a 1:1 ratio to either the MDC or standard of care (SOC). Patients randomized to the MDC were provided monthly multidisciplinary assessment and counseling on exercise, nutrition, and symptom management for 12 months on a rotating schedule. Endpoints included feasibility endpoints (proportion of visits completed), and efficacy endpoints, including mean change from baseline to 12 months in blood pressure (BP), weight, waist circumference, percent body fat, hemoglobin A1C (HbgA1C), insulin resistance, and fasting lipids. Results: 25 men were randomized to MDC, and 23 were randomized to SOC. Overall 91% (295/325) of MDC visits were completed. 72% (18/25) of patients completed all 12 months of MDC, and 80% (20/25) completed the first 6 months. Compared to SOC, patients in the MDC arm had a trend towards more favorable mean percent change from baseline to 12-month follow up in systolic BP (6.5% vs. 10.3%), diastolic BP (-3.9% vs.10.0%), waist circumference (2.5% vs. 4.0%), HbA1C (-2.4% vs. -1.7%), insulin resistance (0.5% vs. 1.9%), and fasting lipids (total cholesterol: 7.0% vs. 21.8%; LDL: -2.9% vs. 7.6%; triglyceride: 15.5% vs. 37.2%). Conclusions: Individualized and comprehensive management of toxicities of ADT in a multidisciplinary clinic is feasible, and appears to provide some benefit over SOC. Larger randomized studies are warranted to investigate whether this intervention will provide lasting benefit. Clinical trial information: NCT02168062.

TPS3126Background: Although multiple new agents have been approved for mCRPC over the last decade, median survival remains unsatisfactory at ~12-35 months. Immunotherapy targeted solely at programm...

TPS5090Background: Men with biochemically relapsed prostate cancer (BRPC) following prior radical prostatectomy (RP) and a short PSA doubling time (PSADT) are at high risk for the development of me...

e17028Background: Ribociclib is a potent and selective cyclin-dependent kinase (CDK) 4/6 inhibitor with significant pre-clinical activity in enzalutamide-resistant prostate cancer cell lines. Prior...

275 Background: New data is emerging to guide primary treatment of patients with metastatic (M+) disease. Among the CHAARTED and LATITUDE cohorts, 27.2% and 5% of patients with M+ disease had prior local therapy, respectively. This study utilizes the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) registry to examine survival among patients with M+ disease. Methods: CaPSURE is a registry of men diagnosed with prostate cancer. We examined sociodemographics, disease biology, primary therapy, and survival among patients who were diagnosed with cM+ disease or developed metastasis. We performed a multivariate Cox model to evaluate the association between timing of metastasis and prostate cancer specific mortality (PCSM), adjusted for age, primary treatment, and follow-up therapy. Results: Of the 14,753 patients diagnosed with prostate cancer from 1990-2016, 717(4.9%) had M+ disease. 328(2.2%) had cM+ disease and 389(2.6%) progressed to bony metastasis. For all patients with M+ disease, 490(68.3%) were > = 65 yo, 627(87.4%) had Medicare, and 239(33.3%) had an annual income < $30,000 (P < 0.01). PSA at diagnosis was > 20 ng/mL for 355(49.5%) and biopsy Gleason was 4+3 or 8 to 10 for 403(56.2%) (P < 0.01). Among patients with cM+ disease, 49(14.9%) received primary local therapy and 279(85.1%) received primary hormonal therapy. Among patients who progressed to M+ disease, 258(66.3%) received primary local therapy and 131(33.7%) received primary hormonal therapy. The risk of PCSM was worse for patients with M+ disease who received hormonal therapy for primary treatment compared to patients who received combined local and hormonal therapy (HR 1.47 (95% CI 1.15 to 1.88), P < .01). Timing of metastatic disease was not associated with PCSM. Primary treatment with hormonal therapy compared to local therapy was associated with higher risk of PCSM (HR 1.40 (95% CI 1.00-1.97), P = 0.05) for patients diagnosed with Gleason > = 4+3 disease. Conclusions: In our analysis, patients with primary local therapy were examined as a subset of all patients with M+ disease. We observed that patients with cM+ disease have a worse prognosis then patients who develop M+ disease with antecedent primary local therapy.

362 Background: A subset of patients (pts) with biochemically recurrent prostate cancer (BRPC) are at risk for metastasis and lethal outcomes, yet many pts wish to defer or avoid androgen deprivation therapy in this setting. Itraconazole has previously demonstrated anti-tumor activity in castration-resistant prostate cancer independent of modulation of circulating androgen levels. We therefore evaluated itraconazole in a phase 2 study in BRPC as a potentially non-castrating treatment approach. Methods: Pts with BRPC and PSA doubling time (PSADT) ≤ 15 months, without metastases on conventional imaging (whole body bone scan + CT/MRI of the abdomen/pelvis), were enrolled in a single arm phase 2 study. Itraconazole was dosed at 300 mg PO BID until PSA progression by PCWG2 criteria, unacceptable toxicity, or pt withdrawal. The primary endpoint was the proportion of pts who achieved ≥ 50% decline from baseline in serum PSA after 12 weeks of protocol therapy. Secondary endpoints included change in PSADT, adverse events (AEs) by CTCAE version 4.0, and change in serum androgens (including testosterone (T) and androstenedione (ASD) from baseline to week 12. Results: 21 pts were enrolled. The median age was 72 (range 54-76), median baseline PSA was 7.6 ng/mL (range 1.5 – 45.5), and median PSADT was 5.7 months (1.2 – 13.0). Median baseline serum T was 336 ng/dL (165-626). Among the 19 evaluable pts, 9 pts (47%) experienced a PSA decline (mean decline 25.0 %, range 2 – 60 %) by week 12, including one patient (5%) with > 50% PSA decline. Among the 10 pts without a PSA decline, the mean on-treatment vs. pre-treatment PSADT was numerically longer (13.2 vs. 4.8 months, p = 0.17). There was no significant change from baseline to week 12 serum T (mean change = 1.9%, p = 0.77) or ASD levels (mean change = 6.1%, p = 0.83). The most common grade ≥ 3 AE was hypertension (29%); hypokalemia of any grade was also common (24%). Conclusions: Itraconazole can modulate serum PSA levels without lowering serum T in pts with BRPC. However, the magnitude of effect is modest and treatment carries an appreciable risk of toxicities related to mineralocorticoid excess. Exploration of the relationship between mineralocorticoid-related AEs, itraconazole drug levels, and clinical outcomes is ongoing. Clinical trial information: NCT01787331.

TPS388 Background: Up to 25% of patients with advanced prostate cancer, including mCRPC, have a deleterious germline or somatic mutation in BRCA1, BRCA2, ATM or another homologous recombination (HR) DNA repair gene that can serve as a molecular marker to select those who may respond to poly(ADP-ribose) polymerase inhibitors (PARPis). PARPis are lethal to cells with HRD, and PARPi treatment has shown preliminary evidence of an antitumor effect in patients with mCRPC who harbor a mutation in an HR DNA repair gene (Mateo et al. N Engl J Med. 2015;373:1697-708). These data provide a compelling rationale for evaluating rucaparib, a potent PARP1, PARP2 and PARP3 inhibitor, in patients with mCRPC associated with HRD. Methods: TRITON2 (NCT02952534) is a phase 2 study evaluating rucaparib 600 mg BID in patients with mCRPC. Patients with a deleterious germline or somatic BRCA1, BRCA2 or ATM mutation (per prior local test or central test during screening) will be enrolled into 1 of 2 cohorts based on the presence or absence of measurable visceral and/or nodal disease. An exploratory cohort will enroll patients with an alteration in any of 12 other prespecified HR genes (eg, RAD51C, RAD51D and PALB2), with or without measurable visceral and/or nodal disease. Patients must have progressed on androgen receptor signaling–directed therapy and 1 prior taxane-based chemotherapy for mCRPC. Patients who received prior treatment with a PARPi, mitoxantrone, cyclophosphamide or platinum-based chemotherapy are excluded. The primary endpoint is objective response rate measured using modified RECIST v1.1/PCWG3 for patients with soft-tissue disease and prostate-specific antigen response for patients with nonmeasurable disease. Secondary endpoints include duration of response, radiographic progression-free survival, overall survival, clinical benefit rate and safety. Pretreatment blood samples collected from all patients will enable development of a plasma-based companion diagnostic to select patients who may benefit from rucaparib treatment. Patients (≈160) will be enrolled at > 100 sites worldwide. Clinical trial information: NCT02952534.

236 Background: Conventional imaging techniques infrequently detect the site of prostate cancer disease in men with biochemical recurrence following radical prostatectomy (RP). We examine the use of Gallium-68 Prostate-Specific Membrane Antigen (PSMA) positron emission tomography (PET) to determine the site of disease recurrence in these men. Methods: We retrospectively reviewed men with persistently detectable prostate specific antigen (PSA) and those with formal biochemical recurrence (PSA ≥ 0.2 ng/mL) following RP who underwent PSMA PET scan under our institution's prospective trials (NCT02918357 & NCT02611882). We assessed the location of detected recurrences, and examined the distribution of recurrence location (prostate bed, pelvic lymph nodes (LN), and extra-pelvic disease) according to PSA at time of PET scan. Results: One hundred and fifty-eight men underwent PSMA PET after RP, 46% of men had previously undergone either adjuvant or salvage radiation therapy. Eleven men (7%) had the scan for persistently detectable PSA < 0.2 and 93% of men had biochemical recurrence. At time of RP, 66% of men had ≥pT3a disease, 40% had positive surgical margins, and 18% had positive lymph nodes. Gleason grade at RP was ≤3+3 in 5% of men, 3+4 in 27%, 4+3 in 32% and ≥4+4 in 36%. Overall, 77% of men had a lesion detectable on PSMA PET. Men with higher PSA at time of scan had a higher prevalence of lesions, with all men PSA > 6.0 having at least one lesion on PSMA PET (Table). Overall, we found extra-pelvic lesions in 44% of all men, and 58% of men with PSA ≥ 1.0. These are areas not typically covered by salvage radiation fields. Conclusions: PSMA PET detects lesions in a high proportion of men with biochemical recurrence following RP, with many lesions outside of the pelvis. This may facilitate more precise targeting of treatment areas for these patients. Clinical trial information: NCT02918357. Clinical trial information: NCT02611882. [Table: see text]

267 Background: Prostate cancer disparities research has largely focused on access to care, treatment, and outcomes. Disparities based on race/ethnicity in clinical trial (CT) participation are less well understood. African American men are known to have an increased risk of developing and dying from prostate cancer compared to their white counterparts yet remain underrepresented in prostate cancer CTs. The goal of this study was to examine the demographic accrual patterns in prostate cancer CTs at an academic cancer center. Methods: A retrospective analysis of demographic data of cancer cases per year was performed from: 1) the central cancer registry of California, Surveillance, Epidemiology, and End Results; 2) new patients (“analytic cases”) identified in the University of California, San Francisco (UCSF) cancer registry; and (3) the UCSF Clinical Trials Management System database. The Catchment Area for the center was prospectively defined, and patients from this region comprised 98% of all cancer cases seen at UCSF. Descriptive statistics were applied to characterize CT accruals for men with prostate cancer relative to cases in our Catchment Area. Results: Overall there were 67,046 new cancer cases of all types in the Catchment Area, of which 6,558 were prostate cancer cases. The distribution of patients with prostate cancer by ethnicity/minority status are summarized (Table). Conclusions: The distribution of minority accruals to prostate cancer CTs conducted at academic cancer centers may not reflect overall accruals to all CTs. At UCSF, the accrual of Latino men with prostate cancer to CTs was representative of the Catchment Area, whereas Asian and Black men were under-represented. These results suggest that tailored, disease-specific interventions are required to achieve equitable CT recruitment.[Table: see text]

TPS389 Background: Recent data have shown that up to 25% of patients with advanced prostate cancer, including mCRPC, have a deleterious germline or somatic mutation in BRCA1, BRCA2, ATM, or another homologous recombination DNA repair gene. Such mutations can be used as a molecular marker to select patients for targeted treatment with poly(ADP-ribose) polymerase inhibitors (PARPis), which are lethal to cells with HRD. Treatment with PARPis has shown preliminary evidence of antitumor activity in patients with mCRPC and a mutation in a homologous recombination DNA repair gene (Mateo et al. N Engl J Med. 2015;373:1697-708). These data provide a compelling rationale for evaluating rucaparib, a potent inhibitor of PARP1, PARP2, and PARP3, in patients with mCRPC associated with HRD. Methods: TRITON3 (NCT02975934) is a randomized, phase 3 study evaluating rucaparib 600 mg BID vs physician’s choice of abiraterone, enzalutamide, or docetaxel in patients with mCRPC and a deleterious germline or somatic BRCA1, BRCA2, or ATM mutation (identified by prior local testing or central testing during screening). Patients must have progressed on androgen receptor signaling–directed therapy in the mCRPC setting; prior PARPi treatment or chemotherapy for mCRPC are exclusion criteria. Patients will be randomly assigned in a 2:1 ratio to either rucaparib or physician’s choice, with the possibility for cross over from the comparator treatment to rucaparib upon radiographic progression confirmed by independent radiology review. The primary endpoint is radiographic progression-free survival (modified RECIST v1.1/PCWG3 criteria) assessed by independent radiology review. Secondary endpoints include objective response rate, duration of response, patient-reported outcomes, overall survival, and safety. Pretreatment blood samples collected from all patients will enable development of a noninvasive plasma-based companion diagnostic to select patients who may benefit from rucaparib treatment. Patients (≈400) will be enrolled at > 100 sites worldwide. Clinical trial information: NCT02975934.

197 Background: The PAM50 gene expression classifier (PAM50) identifies luminal and basal subtypes and predicts response to androgen deprivation therapy in localized prostate cancer. The clinical utility of using PAM50 to molecularly subtype mCRPC was evaluated. Methods: PAM50 was applied to RNA expression data from 86 metastatic tumor biopsies from the SU2C-AACR-PCF West Coast Prostate Cancer Dream Team (WCDT; NCT02432001). Overall survival (OS) differences between luminal A (LuA), luminal B (LuB), or basal patients (pts) were determined using Kaplan-Meier analyses. PAM50 was also applied to 15,136 prospectively collected radical prostatectomy (RP) samples from the Decipher GRiD database (NCT02609269). Drug response signatures (DRS) for 89 drugs were derived using publicly available data from the NCI60 cell line panel, and applied to gene expression data from the RP samples to predict patient-specific drug sensitivities. Differences in DRS as a function of PAM50 subtype were assessed using the Pearson’s chi-squared test. Results: The application of PAM50 to mCRPC transcriptional data segregated pts into LuA, LuB, and basal populations (43%, 14%, and 43%, respectively). The median OS for LuA, LuB, and basal pts was 20.6 months, 9.5 months, and 10.4 months, respectively (p=0.04), which was consistent with localized prostate cancer where LuB pts have the worst prognosis. DRS analyses revealed statistically significant differences in drug sensitivities, with LuA and LuB pts predicted to be markedly more sensitive to docetaxel than basal pts (p

Purpose Mitoxantrone plus prednisone and ixabepilone each have modest activity as second-line chemotherapy in docetaxel-refractory castration-resistant prostate cancer (CRPC) patients. Clinical noncrossresistance was previously observed. Patients and Methods Metastatic CRPC patients progressing during or after taxane-based chemotherapy enrolled in a phase I multicenter study of ixabepilone and mitoxantrone administered every 21 days along with prednisone. Ixabepilone and mitoxantrone doses were alternately escalated in a standard 3 + 3 design. Patients were evaluated for toxicity and disease response. Dose-limiting toxicities (DLTs) were defined as treatment related, occurring during cycle 1, and included grade 4 prolonged or febrile neutropenia, thrombocytopenia (grade 4 or grade 3 with bleeding), or ≥ grade 3 nonhematologic toxicity. Results Thirty-six patients were treated; 59% of patients experienced grade 3/4 neutropenia. DLTs included grade 3 diarrhea (n = 1), prolonged grade 4 neutropenia (n = 4), and grade 5 neutropenic infection (n = 1). Due to prolonged neutropenia, the highest dose levels were repeated with pegfilgrastim on day 2 of each cycle. The maximum tolerated dose in combination with pegfilgrastim was not exceeded. The recommended phase II dose is mitoxantrone 12 mg/m2 and ixabepilone 35 mg/m2 every 21 days, pegfilgrastim 6 mg subcutaneously day 2, and continuous prednisone 5 mg twice per day. Thirty-one percent of patients have experienced ≥ 50% prostate-specific antigen (PSA) declines, and two experienced objective responses. Of 21 patients treated with mitoxantrone 12 mg/m2 plus ixabepilone ≥ 30 mg/m2, nine (43%) experienced ≥ 50% PSA declines (95% CI, 22% to 66%). Conclusion These results suggest that the combination of ixabepilone and mitoxantrone is feasible and active in CRPC and requires dosing with pegfilgrastim.

The purpose of this review is to discuss the recent increase in data supporting the use of androgen ablation early in the clinical course for patients with nonmetastatic prostate cancer. We systematically reviewed recent publications that report on the use of androgen deprivation (AD) in nonmetastatic prostate cancer patients from the 2003 and 2004 procedings of the American Society of Clinical Oncology, the 2003 and 2004 procedings of the American Urological Association as well as published literature from 2003 to 2005. Five recently published mature randomized trials of AD plus local therapy were evaluated plus two large data sets on the use of AD for patients with serologic relapse after local therapy. Four mature randomized studies demonstrate an overall survival benefit to the use of AD in conjunction with definitive local therapy (three with radiation and one with surgery). One retrospective analysis suggests that AD administered early after serologic progression improves overall survival, and one retrospective analysis shows a reduction in metastasis-free survival but has not yet shown an overall survival benefit. For patients with nonmetastatic prostate cancer with high-risk features, as well as those for serologic relapse, the use of AD before the development of metastatic disease is supported by long-term outcomes from a series of clinical trials. Consideration of AD is therefore warranted early in the clinical course of high-risk patients.

Recently, data from two randomized phase III studies that compared docetaxel-based chemotherapy to mitoxantrone-based therapy demonstrated that treatment with docetaxel can prolong life in a significant way for patients with hormone-refractory prostate cancer. For many patients who experience disease progression after androgen-deprivation therapy, however, chemotherapy may not be immediately indicated. Such cases include those individuals with hormone-refractory disease in the absence of clinical metastases, and those with asymptomatic metastatic disease, for example. As a result, clinicians treating patients with hormone-refractory disease must weigh the benefits of earlier chemotherapy against its risks, and may consider other therapies such as secondary hormonal approaches before initiating chemotherapy. This decision is further complicated by the fact that a phase III study designed to compare secondary hormonal therapy with chemotherapy has failed due to lack of accrual. Furthermore, the limitations of chemotherapy for prostate cancer are being clarified and include a lack of standard second-line therapy as well as uncertain benefits for those with nonmetastatic disease. In this review, we will highlight some of the issues that impact on the decision of when to start chemotherapy and in whom as well as the potential benefits of secondary hormonal approaches.

TPS5087 Background: Pts with mCRPC often initially receive androgen receptor-targeted therapy (eg, abiraterone or enzalutamide), but they almost always progress. Poly(ADP-ribose) polymerase (PARP) inhibitors (eg, olaparib) have demonstrated clinical activity in pts with mCRPC with a deleterious mutation in a homologous recombination (HR) DNA repair gene; 14 of 16 evaluable pts with mCRPC and a tumor alteration in an HR gene, including BRCA1, BRCA2, and ATM, responded to olaparib (Mateo et al. N Engl J Med. 2015;373:1697-708). The PARP inhibitor rucaparib is approved in the US for treatment of pts with ovarian carcinoma that harbors a deleterious BRCA1 or BRCA2 mutation (germline and/or somatic) who have received ≥2 chemotherapies. These data support investigating rucaparib as a treatment option in pts with mCRPC with HRD. Methods: TRITON3 (NCT02975934)is a phase 3 study evaluating rucaparib (600 mg BID) vs physician’s choice (abiraterone, enzalutamide, or docetaxel) in pts with mCRPC who have a deleterious germline or somatic mutation in BRCA1, BRCA2, or ATM as determined by local and/or central testing. All pts must have progressed on abiraterone or enzalutamide in the mCRPC setting; pts who received prior chemotherapy for mCRPC or PARP inhibitor treatment are excluded. Pts will be randomized 2:1 to rucaparib or physician’s choice of comparator therapy; pts randomized to physician’s choice may cross over to rucaparib on radiographic progression confirmed by independent radiology review (IRR). The primary endpoint is IRR-confirmed radiographic progression-free survival (modified RECIST version 1.1/PCWG3 criteria). Secondary objectives include overall survival, objective response rate, duration of response, clinical benefit rate, pt-reported outcomes, and safety. Pretreatment blood samples will be collected from all pts to enable development of a plasma-based companion diagnostic to identify pts who may benefit from rucaparib treatment. Pts (≈400) will be enrolled at > 100 sites worldwide. Clinical trial information: NCT02975934.

5056 Background: Standard imaging in early stage PC has focused on detecting metastases (mets) within the abdomen and pelvis. The incidence of IT mets (lung, mediastinal, or supraclavicular) mets is unknown, but presumed to be negligible. Whole body 68Ga-PSMA PET has greater sensitivity compared to conventional imaging, affording the opportunity to estimate the incidence of IT mets. Methods: Newly diagnosed or biochemically recurrent (BCR) PC patients (pts) with apparent localized disease on standard imaging were enrolled on a prospective study of 68Ga-PSMA PET imaging between June 2015 and January 2017 and were analyzed for incidence of IT mets. Positive lesions were defined as uptake higher than blood pool. When appropriate, patients underwent confirmatory biopsy of the PSMA-avid IT lesions. Results: 364 pts underwent 68Ga-PSMA PET imaging, including 121 (33%) pts with newly diagnosed PC and 243 (67%) pts with BCR. 145 pts (40%) had at least 1 PSMA-avid metastasis. PSMA-avid IT mets were detected in 20 pts (5.5% of overall cohort; 13.8% of those with ≥ 1 PET-positive mets), including 3 newly diagnosed (2.5%) pts and 17 (7.0%) pts with BCR. 9 of 20 pts (45%) had IT mets as the only detectable site of metastasis on PET. Biopsy of the PSMA-avid IT lesion was found to harbor PC in 5/5 patients (100%). Sites of detection included: supraclavicular node, n = 9 (2.5%); mediastinal node(s), n = 10 (3.6%), and visceral lung, n = 4 (1.0%). In the entire study cohort of 364 pts, 43% of pts had a Gleason Score ≥ 8 at diagnosis, median PSA was 4.87 ng/mL (range: 0.04 – 83.7), and the median PSA doubling time was 6.2 months (range: 0.4 – 78.3) in patients with BCR. There were no significant differences in PSA, PSA doubling time, Gleason grade, or stage between patients harboring IT metastases vs. those who did not. Conclusions: IT mets are detected by 68Ga-PSMA PET imaging at an appreciable frequency in early stage PC with apparent localized disease by conventional imaging, which may significantly impact management in these cases. Further studies are warranted to validate these findings and determine the optimal strategy for the detection and treatment of supradiaphragmatic metastases in newly diagnosed and biochemically recurrent PC. Clinical trial information: NCT02918357.

5067 Background: Higher baseline androgens have been previously shown to be associated with an improved overall survival (OS) in mCRPC patients treated with the androgen synthesis inhibitors, ketoconazole or abiraterone. The purpose of this analysis was to determine whether baseline serum androgen levels (Testosterone (T), Androstenedione (A) and DHEA (D) are associated with OS in mCRPC patients treated with docetaxel-based chemotherapy. Methods: Data from 1,050 men treated on CALGB 90401 with docetaxel, prednisone and either bevacizumab or placebo were used. Eligibility required progressive mCRPC and no prior chemotherapy. Pre-treatment serum assays for T, A and D were performed via tandem Liquid Chromatography-Mass Spectrometry (LC-MS/MS) at NMS labs. The proportional hazards model was used to assess the prognostic significance of T, A, and D in predicting OS adjusting for known prognostic factors. Results: Median values for T, A, and, D were 1.00, 13.00 and 8.12, ng/dL respectively.Values above the median were defined as low, above as high. Median OS for low vs high levels was 22.7 and 23.1 month for T, 22.4 and 21.7 month for A and 21.8 and 24.0 month for D, respectively, all NS. In multivariable analysis adjusting for 10 known prognostic values and prior keto use in mCRPC (Halabi JCO 2014), A (p-value = 0.013) levels were associated with OS. The HR for A was = 0.99 (95% CI = 0.98-0.99). Conclusions: In multivariate analysis, baseline androstenedione levels are prognostic factors for OS in mCRPC patients receiving chemotherapy. Low or undetectable levels of other androgens are associated with shorter OS, consistent with prior results in androgen synthesis inhibitor treated pts in both the chemotherapy naive and post chemotherapy settings. This relationship may reflect more aggressive tumor biology that evolves in an extreme androgen deprived milieu. Clinical trial information: NCT00110214.

e16533 Background: Patients (pts) with abiraterone (abi) or enza (enza) refractory mCRPC typically have limited treatment options. Selinexor is a first in class SINE that specifically inhibits the nuclear export protein Exportin-1 (XPO-1) which is overexpressed in prostate cancer (PCa), leading to cytoplasmic mislocalization of tumor suppressor proteins. In preclinical models of PCa, selinexor reduced tumor growth and decreased the incidence of bone metastasis. Methods: Eligibility criteria included progressive mCRPC with primary or acquired resistance to abi, enza, or their combination. Prior chemotherapy for mCRPC was not allowed. All pts must have > 1 bone metastasis. The primary objective was radiographic progression free survival (rPFS). Results: Fourteen pts were enrolled between Oct 2014 and Oct 2016. The median age was 72 years (range 56-79) and median baseline PSA was 73.8 ng/mL (range 12.8-686.9). Eleven pts (79%) had both prior abi and enza. The initial selinexor dose was 65 mg/m2 on Day 1 (D1) and Day 3 (D3) weekly. For toxicity concerns, after the first 2 pts, dose was reduced to 60 mg on D1 and D3 for the first 3 wks followed by a 1-wk rest period (28-day cycle). All pts received ondansetron and olanzapine to prevent nausea and anorexia. The median treatment duration was 3 cycles (range 1-12), and median follow-up was 4 months. One pt (7.1%) had > 50% PSA decline, 5 pts (35.7%) had > 30% PSA decline, and 7 pts (50%) had any PSA decline. Of 10 pts evaluable, 9 pts had stable disease as best radiographic response, and 1 pt had progressive disease on the first radiographic evaluation. The median rPFS was 3.6 months (95% CI 2.1-not reached). The most common AEs of any severity were anorexia (86%), nausea (64%), weight loss (50%), fatigue (50%), thrombocytopenia (50%), anemia (36%), and vomiting (36%). Grade 3/4 AEs included nausea (14%), vomiting (14%), anemia (14%), anorexia (7%), weight loss (7%), thrombocytopenia (7%) and neutropenia (7%). Conclusions: Selinexor demonstrated limited clinical activity in mCRPC. Toxicity, in particular anorexia and weight loss, hinders further development in this pt population. Clinical trial information: NCT02215161.

5057 Background: PET imaging of prostate specific membrane antigen (PSMA) has been shown to have a higher sensitivity and specificity compared to conventional imaging. The objective was to evaluate the impact of PSMA PET on the management of prostate cancer patients with biochemical recurrence following local therapy. Methods: In our initial Ga-68-PSMA-11 PET protocol (NCT02611882), 150 patients with biochemical recurrence were imaged. 63 patients were imaged using PET/CT (GE Discovery VCT) and 63 patients using PET/MRI (GE Signa 3.0T PET/MRI). 110 patients received Lasix injections. Referring clinicians filled out a pretreatment management form and a management form based on the imaging results. Changes in management were graded as major, minor, no change or unknown based upon the responses. Results: We received both pre and post imaging forms in 126 patients, for an 84% response rate. The average PSA in the population was 5.9 ± 5.4 ng/mL with an average doubling time of 9.7 ± 11.0 months, and 60 patients had a PSA of less than 2.0 at the time of imaging. The average time between prior treatment and imaging (RP and/or radiation) was 5.3 ± 5.4 years, with 46 patients imaged within two years of their most recent treatment. 43 patients had a prior prostatectomy, 41 prior radiation, and 33 patients had both. 103 patients (82%) had disease localized on PSMA imaging. Of the 126 patients, 67 (53%) of the imaging studies resulted in a major change in management. The most common major change was converting from active surveillance to radiation therapy (15 patients, 12%), changing from ADT to radiation therapy (16 patients, 13%), and converting from radiation therapy to either active surveillance (6 patients, 5%) or to ADT alone (3 patients, 2%). 10 patients (8%) had a minor change, 42 patients (33%) had no change, and 7 patients (6%) had an unknown change in management. Conclusions: The results of our surveys demonstrate a substantial impact of PSMA PET on the intended patient management. The majority of changes involved converting a targeted therapy to systemic treatment or systemic treatment to a targeted therapy. Prospective studies are warranted to determine whether directed treatment towards PSMA-avid lesions affects long-term disease outcomes. Clinical trial information: NCT02611882.

154 Background: Interactions between metastatic prostate cancer cells, osteoblasts, osteoclasts, and other participants in bone metabolism are complex and result in pathologic bone physiology. Ra-223, a targeted alpha therapy, accumulates at sites of bone metastases and prolongs survival. Ra-223 and docetaxel (D), acting through different mechanisms of action, may have beneficial effects on bone pathophysiology and tumor microenvironment. Prior data suggest treatment with Ra-223 results in favorable alterations in bone biomarkers that are associated with survival. Methods: 53 patients with progressing CRPC and ≥ 2 bone metastases were randomized 2:1 to Ra-223 (55 kBq/kg q6wk × 5) + D (60 mg/m2 q3wk × 10) versus D (75 mg/m2 q3wk with step-down option to 60 mg/m2). Bone resorption (CTX-1, ICTP) and formation (P1NP, bALP) markers, tALP, and PSA were analyzed at wk 19 (after 3 Ra-223 injections) and 3 wk after end of treatment (EOT). Results: Mean % change at wk 19 and EOT are shown (Table). tALP, bALP, P1NP, and PSA declined early during treatment, reaching an average of > 30% decline from baseline by wk 19 in both arms. Mean % declines were greater in the Ra-223 + D versus the D-alone arm at wk 19 and EOT. Bone resorption markers CTX-1 and ICTP showed little decline at wk 19. Conclusions: Ra-223 + D patients had greater % decline in tALP and in bone formation markers bALP and P1NP. Due to small patient numbers and preliminary data, further analysis and correlation with clinical outcomes in a larger study is warranted. Clinical trial information: NCT01106352. [Table: see text]

3 Background: There is a clear need to develop a clinically relevant molecular subtyping approach for prostate cancer. We hypothesized that prostate cancer can be subtyped based on luminal versus basal lineage. Methods: We applied the PAM50 classifier, which is used clinically to identify luminal and basal cancers in breast cancer, to subtype a total of 3,782 prostate cancer samples using a high-density microarray platform run in a CLIA-certified laboratory. We examined the associations of these subtypes and clinical outcomes. Results: We demonstrate that PAM50 segregates prostate cancer into three reproducible subtypes in both retrospective cohorts and on prospective validation: luminal A (33.3%-34.3%), luminal B (28.5%-32.6%), and basal (34.1%-37.1%). Luminal B prostate cancers exhibited the worst clinical prognoses, followed by basal and luminal A subtypes (10-year biochemical recurrence-free survival: 29/39/41%; distant metastasis-free survival: 53/73/73%; prostate cancer-specific survival: 78/86/89%; overall survival: 69/80/82% respectively) on both univariable and multivariable analyses accounting for standard clinicopathologic prognostic factors. Known luminal lineage markers, such as NKX3.1 and KRT18, and the basal lineage CD49f signature, were enriched in luminal- and basal-like cancers respectively, demonstrating the connection between these subtypes and established prostate cancer biology. While both luminal-like subtypes were associated with increased AR expression and signaling, only luminal B prostate cancers were significantly associated with post-operative response to androgen deprivation therapy (ADT) in a subset analysis matching patients based on clinicopathologic variables (interaction p = 0.006, luminal B 10-year metastasis: 33% (treated) vs. 55% (untreated), non-luminal B: 37% (treated) vs. 21% (untreated)). Conclusions: These findings contribute novel insight into the biology of prostate cancer, and provide translatable clinical tools for personalizing post-operative ADT for patients with prostate cancer. Similar to breast cancer, these findings suggest that luminal/basal subtyping may be useful in treatment selection in prostate cancer.