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124 Background: Biomarker testing for EGFR mutations (EGFRm) is recommended for all newly diagnosed patients with metastatic NSCLC. Third-generation EGFR TKIs are the recommended standard-of-care therapy for patients with EGFRm+ NSCLC regardless of race, although EGFRm occur more frequently in Asian patients (Table). We investigated the association between race, EGFR testing and receipt of subsequent first-line (1L) treatment with the third-generation EGFR TKI, osimertinib. Methods: This retrospective, observational study used the nationwide Flatiron Health EHR-derived de-identified database. Adults with an initial diagnosis of stage IV NSCLC who initiated systemic 1L therapy between Apr 2018 (osimertinib approval) and Feb 2022 (data cutoff date) were eligible. Two cohorts were defined: those eligible for EGFR testing, and those EGFRm+ patients eligible for 1L osimertinib. Multivariable logistic regression was used to investigate odds of 1) EGFR testing, and 2) 1L osimertinib use, by race. Random-effects logistic regression was used as a sensitivity analysis to evaluate the impact of inter-practice variation on each outcome. Confidence intervals (CI) were calculated at 95%. Results: 9,505 patients were eligible for EGFR testing. After adjustment, Asian patients were nearly twice as likely to be tested (adjusted odds ratio [aOR]: 1.93, CI: 1.33 – 2.89, p = 0.0001), while Black patients were 25% less likely to receive testing (aOR: 0.75, CI: 0.62 – 0.90, p = 0.002), both relative to White patients. Including a random factor of practice attenuated the effect of race for Asian patients (aOR: 1.74, CI: 1.15 – 2.64, p = 0.0009) as well as Black patients (aOR: 0.8, CI: 0.65-0.97, p = 0.021). Of these patients, 1,247 were confirmed EGFRm+ and were thus eligible for 1L osimertinib. Asian patients were marginally more likely to receive 1L osimertinib, even after adjustment ( aOR: 1.51, CI: 0.958 – 2.43, p =.082). The inclusion of a random factor of practice diminished the marginal effect of race ( aOR: 1.46, CI: 0.90 – 2.36, p = 0.1). Conclusions: Retrospective analyses using real-world data revealed differences across races in EGFR testing among patients with stage IV NSCLC, suggesting disparities in quality of care. Racial disparities were also observed in 1L osimertinib use among patients with EGFRm+. Sensitivity analyses suggest that these disparities may partially be attributed to differences in care between practices. Future studies are warranted to further characterize this unexpected race-based difference in biomarker testing and treatment initiation. This work highlights the need for investigations of racial disparities in access to both biomarker testing and effective treatment options across precision oncology.[Table: see text]

INTRODUCTION AND OBJECTIVES:Malignant pheochromocytomas (MP) are a rare form of endocrine malignancy which can occur in familial and sporadic clinical settings. We performed comprehensive genomic p...

INTRODUCTION AND OBJECTIVES:Relapsed and metastatic penile (mPSCC) and uterine cervical squamous cell carcinoma (mCSCC) are aggressive forms of malignancy with currently limited systemic treatment ...

9566 Background: We performed a comprehensive genomic profiling (CGP) study of AM and CM to learn of potential genomic alterations (GA) linked to targeted and immune checkpoint inhibitor (ICPI) therapies. Methods: 90 AM and 1804 CM FFPE tissues from late stage underwent hybrid-capture based CGP to evaluate all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on up to 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. PD-L1 expression was determined by IHC. Results: AM and CM had a similar age, but AM females and CM males were significantly more common (P < 0.0001). GA/tumor was significantly higher in CM (UV light exposure) as were the median TMB and frequency of TMB ≥ 10 and 20 mutations/Mb (P < 0.0001 for all comparisons). PD-L1 expression was higher in AM than CM (P = 0.0023). AM and CM were all MS-stable. The contrast in S FB1 mutations in AM and TERT GA in CM were significant (P < 0.0001). Of potentially targetable GA, AM featured significantly more KIT GA than CM (P < 0.0001), whereas CM featured significantly more BRAF GA (P < 0.0001). Only 11% of AM BRAF GA were V600E whereas 74% of CM BRAF GA were V600E (P < 0.0001). MTOR pathway GA were common in both tumor types. Additional potentially targetable alterations in PDGFRA and ERBB2 kinases were seen in AM but not in CM. Conclusions: CM is distinct from AM featuring higher GA/tumor, higher TMB and frequent BRAF V600E GA that predict benefit from ICPI and anti-BRAF therapies. Although both AM and CM feature MTOR pathway targets, AM does have higher PD-L1 expression than CM and is characterized by an array of potentially targetable kinase genes including KIT, PDGFRA, ERBB2 and to a lesser extent than CM, BRAF.[Table: see text]

e15565 Background: KRAS mutations are common oncogenic events across cancers, but effective RAS-directed therapies are lacking. However, recent studies support use of PD-1 blockade in most subsets of lung cancer with KRAS short variant mutations (KRASSV) (PMID: 28039262), and preclinical data supports combined MEK and SHP2 inhibition in KRAS amplified ( KRASa) GEA (PMID: 30093730). We sought to explore the landscape of KRAS altered GEA and compare genomic profiles of KRAS-altered and KRAS wild-type (WT) cases for biomarkers of response to targeted therapies and immune checkpoint inhibitors. Methods: 6,667 tissue specimens from patients with advanced GEA were assayed using hybrid capture-based comprehensive genomic profiling. Tumor mutational burden (TMB) was determined on up to 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 95 or 114 loci. Descriptive statistics were used to compare among subgroups. Results: KRASSV and KRASa were identified in 11% and 5.8% of gastric adenocarcinoma (GA), respectively, and in 7.2% and 17% of esophageal adenocarcinoma (EA), respectively. KRASa and KRASSV were nearly mutually exclusive, co-occurring in only 4.4% of KRAS altered cases. ERBB2 alterations were less common in KRASSV and KRASa GEA (both 9%) as compared with KRAS WT GEA (19%) (p = 1.9E-16). EGFRa was less common in KRASSV vs KRASa GEA (1.9% vs 9.3%, p = 2.6E-8), whereas PIK3CASV was more common in KRASSV vs KRASa (16% vs 5.0%, p = 1.5E-11). Median TMB for all groups was similar; however, KRASSV GEA had a higher mean TMB (9.7 mut/Mb) as compared to KRASa (5.1 mut/Mb, p = 5.0E-12) and KRAS WT cases (5.8 mut/Mb, p = 2.2E-07). KRAS codon 12/13 accounted for > 80% of predicted pathogenic mutations. MSI-high was also more prevalent in KRASSV (11.3%) vs KRASa (0.9%, p = 4.8E-15) and KRAS WT GEA (2.4%, p = 1.8E-25). MSI-high KRASSV GEA was associated with older patient age (median 72 years) and with high TMB (median 40.9 mut/mb). Conclusions: GA was enriched for KRAS mutation whereas EA was enriched for KRAS amplification. KRAS WT vs KRASSV vs KRASa each presented distinct genomic profiles. KRASa in the absence of KRAS mutation exists in 11% of GEA and warrants further exploration to inform combination treatment strategies.

532 Background: Metastatic testicular sex cord stromal tumors of the testis (MSCST) comprise an extremely uncommon form of genitourinary malignancy. In a comparative genomic study, we performed comprehensive genomic profiling (CGP) to characterize the genomic alterations (GA) in MSCST and to enable the search for potential therapy targets. Methods: The MSCST were classified as metastatic Leydig Cell Tumors (LCT), Sertoli Cell Tumors (SCT) and Undifferentiated (USCST). In this study, 10 cases of LCT, 6 cases of SCT and 3 cases of USCST underwent hybrid-capture based CGP to evaluate all classes of genomic alterations. Tumor mutational burden (TMB) was determined on 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Results: All patients had clinically advanced recurrent and/or metastatic disease. The primary testis tumor was used for sequencing in 6 MSCST (32%) and a metastatic site in 9 (68%) of the MSCST. In 10 (91%) of 11 MSCST positively stained by IHC for inhibin expression. The overall frequencies of GA were similar in all LCT, SCT and UTST ranging from 3.0 to 3.5 GA/tumor. The most frequent untargetable GA found in all MSCST cases included CTNNB1 and CDKN2A/B, both ranging from 20-33% of cases. Targetable GA were uncommon in all MSCST sub-groups but several tumors featured potential for cell cycle inhibitors ( CDK4 in LCT), MTOR inhibitors ( RICTOR, NF2 and PTEN in all 3 tumor types), hedgehog inhibitors ( PTCH1 in LCT) and PARP inhibitors ( BAP1 in SCT). No MSI-High status was identified in any MSCST. The TMB was also low in all MSCST groups. Conclusions: Although the 3 subgroups of testicular MSCST feature defining histopathologic features, these tumors have similar genomic signatures on CGP. The low levels of GA per tumor, infrequent tumor aneuploidy, absence of MSI-High status and low TMB all indicate that testicular MSCST are genetically stable. However, rare cases of testicular MSCST reveal GA linked to potential targeted therapy benefits on CGP linked to dysregulation of multiple biologic pathways. In contrast, the lack of MSI-High status and overall low TMB in testicular MSCST indicates a likely lack of benefit for immunotherapies for these rare forms of malignancy.

514 Background: Metastatic penile (mPSCC) and uterine cervical squamous cell carcinoma (mCSCC) are aggressive forms of malignancy with limited treatment options. We used comprehensive genomic profiling (CGP) to compare the genomic alterations (GA) and their potential impact on targeted and immunotherapy options of mPSCC and mCSCC. Methods: 78 metastatic mPSCC and 604 mCSCC underwent CGP using a hybrid-capture-based next-generation sequencing assay with a mean coverage depth of > 500X. Tumor mutational burden (TMB) was determined on 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Results: The median age of mPSCC men was higher than mCSCC women. The HPV+/CDKN2A- status was more frequent in the mCSCC than mPSCC. The GA/tumor were similar for both tumor types (table). TP53 mutations were more common in mPSCC likely linked to loss of original HPV+ status. TERT, NOTCH1 and FAT1 GA were more frequent in mPSCC whereas PIK3CA GA were more common in mCSCC. MTOR pathway targets (GA in STK11, FBXW7 and PTEN) were more common in mCSCC. MSI-High status was extremely rare in all cases, but the relatively high frequencies of TMB ≥ 10/20 mut/Mb in both mPSCC and mCSCC were noteworthy. Examples of patients with mCSCC and mPSCC responding to targeted and immunotherapies will be presented. Conclusions: Although mCSCC and mPSCC share a variety of genomic features, the 2 tumor types can nonetheless be sharply differentiated on CGP. The TP53, CDKN2A and HPV status of the tumor types differ significantly with viral identification much higher in the mCSCC group. There are opportunities for targeted therapies in both groups predominantly identified in the MTOR pathway. Numerous cases with significantly elevated TMB in both mPSCC and mCSCC suggest that immunotherapies might be of benefit in a subset of patients. [Table: see text]

508 Background: Malignant pheochromocytomas (MP) are a rare form of endocrine malignancy which can occur in familial and sporadic clinical settings. We performed comprehensive genomic profiling (CGP) to characterize the genomic alterations (GA) in MP and to enable the search for potential therapy targets. Methods: From a series of 181,782 consecutive clinical cases, 43 cases of clinically advanced MP underwent CGP using a hybrid-capture based commercial assay to evaluate all classes of GA. Tumor mutational burden (TMB) was determined on 1.1 Mbp of sequenced DNA and reported as mutations/Mb and microsatellite instability (MSI) was determined on 114 loci. IHC for PD-L1 expression was performed on a subset of patients (DAKO 22C3 antibody). Results: All patients had clinically advanced recurrent and/or metastatic disease. There were 33 (77%) of MP known to have originated in the adrenal gland and 10 (23%) of the MP were sequenced from metastatic site. The primary tumor was used for sequencing in 13 (30%) of the MP cases and a non-primary tumor metastatic site (liver, lung, bone, soft tissue, lymph node, kidney, peritoneal cavity, and chest wall) in 30 (70%) of the MP cases. There were 2.3 GA/tumor. The most frequent un-targetable GA were ATRX (26%), TP53 (21%), SDHB (11%), CTNNB1 (7%), VHL (7%), and CDKN2A/2B, PIK3R2, NOTCH2 and MEN1 (all 5%). The most frequent potentially targetable GA included RET (9%), NF1 (9%) and FGFR1 (5%). PBRM1 GA were found in 2% of MAP. Germline mutations in known cancer predisposition genes were predicted in 7 (16%) of cases involving SDHB (4 cases) and BRCA1, MEN1, and MSH2 (1 case each). The mean TMB was 2.95 mutations/Mb, the median TMB was 2.4 mutations/Mb. 0 (0%) of 33 MP evaluated for MSI had a MSI-High status. Conclusions: MP represent a rare form of endocrine cancer that feature a variety of genomic alterations. Although the GA/tumor is relatively low for MP, CGP can reveal important potential targets for therapy in the metastatic setting including RET, NF1 and FGFR1. MAP do not reveal strong potential for immunotherapy with low TMB, absence of MSI-High status and low (2%) PBRM1 mutation frequencies. Based on this data, further study of CGP as a method of developing precision therapies for MP appears warranted.

271 Background: Prostatic ductal carcinoma (PDC) is an uncommon centrally located prostate with a characteristic tubulopapillary histology. PDC shares some biomarker features with the more common prostatic acinar carcinoma (PAC) including PSA expression. Methods: In this comparative comprehensive genomic profiling (CGP) study, FFPE samples from 61 clinically advanced PDC and 4,132 PAC were profiled for all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Results: The age, frequency of genomic alterations (GA) per tumor and TP53 GA of PDA and PAC were similar (Table). TMPRSS2:ERG fusions and AR GA were more often identified in PAC than PDC whereas PTEN GA were more common in PDC than PAC. Targetable GA were identified at similar frequencies in both groups focused on BRCA2 (PARP inhibitors), BRAF (BRAF/MEK inhibitors) and PIK3CA (MTOR inhibitors). ATM GA (PARP inhibitors) were more common in PAC than PDC. CDK12 GA potentially associated with immunotherapy (IO) benefit were similar in PDA and PAC as were the frequencies of MSI-High status, median TMB and high TMB levels. Conclusions: The pathologic features of PDC and PAC have been classically maintained as representative of 2 different tumor types with potentially contrasting histogenesis. In the current CGP-based study, PDA and PAC did not display significant differences in genomic signatures. CGP may reveal biomarkers that could direct patients to targeted (PARP, MTOR and BRAF/MEK inhibitors) or immunotherapies ( CDK12 GA, MSI-High or high TMB status) in both PDA and PAC. [Table: see text]

132 Background: Prostatic ductal carcinoma (PDC) is an uncommon centrally located prostate with a characteristic tubulopapillary histology. PDC shares some biomarker features with the more common prostatic acinar carcinoma (PAC) including PSA expression. Methods: In this comparative comprehensive genomic profiling (CGP) study, FFPE samples from 61 clinically advanced PDC and 4,132 PAC were profiled for all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Results: The age, frequency of genomic alterations (GA) per tumor and TP53 GA of PDA and PAC were similar (Table). TMPRSS2:ERG fusions and AR GA were more often identified in PAC than PDC whereas PTEN GA were more common in PDC than PAC. Targetable GA were identified at similar frequencies in both groups focused on BRCA2 (PARP inhibitors), BRAF (BRAF/MEK inhibitors) and PIK3CA (MTOR inhibitors). ATM GA (PARP inhibitors) were more common in PAC than PDC. CDK12 GA potentially associated with immunotherapy (IO) benefit were similar in PDA and PAC as were the frequencies of MSI-High status, median TMB and high TMB levels. Conclusions: The pathologic features of PDC and PAC have been classically maintained as representative of 2 different tumor types with potentially contrasting histogenesis. In the current CGP-based study, PDA and PAC did not display significant differences in genomic signatures. CGP may reveal biomarkers that could direct patients to targeted (PARP, MTOR and BRAF/MEK inhibitors) or immunotherapies ( CDK12 GA, MSI-High or high TMB status) in both PDA and PAC. [Table: see text]

551 Background: Anal melanomas (AM) share histologic features with cutaneous melanomas (CM), are highly aggressive and behave in a distinct clinicopathologic pattern. We performed comprehensive genomic profiling (CGP) of AM to learn of potential matched targeted and immunotherapies that may improve clinical outcomes for the disease. Methods: FFPE tissues from late stage AM (81 cases) and CM (1804 cases) underwent hybrid-capture based CGP to evaluate all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on up to 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Results: AM and CM had a similar age, but AM females and CM males were significantly more common (P < 0.0001) (Table). Given the UV light exposure in the CM, the GA/tumor was significantly higher than AM as were the median TMB and frequency of TMB ≥ 10 and 20 mutations/Mb (P < 0.0001 for all comparisons). All AM and CM were MS-stable. The contrast in S FB1 mutations in AM and TERT GA in CM were significant (P < 0.0001). AM featured significantly more KIT GA than CM (P < 0.0001), whereas CM featured significantly more BRAF GA (P < 0.0001). Only 11% of AM BRAF GA were V600E whereas 74% of CM BRAF GA were V600E (P < 0.0001). MTOR pathway targets including NF1 and PTEN were commonly altered in both tumor types. Potentially targetable PDGFRA and ERBB2 GA were found in AM but not in CM. Conclusions: UV light exposure drives high GA/tumor and TMB in CM, both associated with immune checkpoint inhibitor (ICPI) responsiveness, whereas AM lacks the high TMB and therefore is far less likely to benefit from ICPI treatments. CM is classically associated with opportunities for anti-BRAF therapies and AM with an array of kinase targets including KIT, BRAF, PDGFRA and ERBB2. Finally, MTOR pathway targets are common to both tumor types. [Table: see text]

12091Background: PBRM1, a member of the SWI/SNF family, is involved in chromatin remodeling. Recent evidence indicates that PBRM1 inactivating mutations are associated with clinical benefit from immune checkpoint inhibitor treatments in clear cell renal cell carcinoma (ccRCC). Methods: CGP was performed on 140,411 specimens from solid tumors and hematologic malignancies using a hybrid capture-based NGS assay. Profiles were assessed for neoantigen load, tumor mutational burden (TMB), determined on 1.1 Mbp of sequenced DNA, and microsatellite instability (MSI) determined by principal components analysis of optimal homopolymer loci. Genomic alterations (GA) in PBRM1 considered here were known loss-of-function GA or homozygous GA in the tumor. Results: PBRM1 GA were identified in 3,674 (2.6%) cases. Compared to other tumor types, the PBRM1 GA frequency was significantly higher in ccRCC at 45% (P < 0.0001); other tumor types with frequent PBRM1 GA were renal cell carcinoma NOS (27%), site-specific mesothelioma...

5061Background: We hypothesized that sub-categorization of TMPRSS2 fusion status would impact therapy opportunities in patients with clinically advanced CRPC and CRNEPC. Methods: CGP was performed ...

11553Background: In an exploratory study to find biomarkers for both targeted and immunotherapy treatments, we performed CGP on a series of PSRC to search for novel therapy options for patients wit...

8562Background: PBRM1, of the SWI/SNF family, modulates chromatin remodeling. PBRM1 genomic alterations (GA) are enriched in renal cell carcinoma and mesothelioma (MS). Recent evidence suggests tha...

6089Background: Anaplastic thyroid carcinoma (ATC) is a rare malignancy with a poor prognosis. We queried whether comprehensive genomic profiling (CGP) could uncover biomarkers that could enable ta...

3574Background: High levels of microsatellite instability (MSI-H) is an approved biomarker for the selection of immunotherapy across solid tumor types. Given the high prevalence of MSI high in CRC,...

9587Background: Carcinomas that arise from the skin adnexae (Cutaneous Adnexal Carcinomas, CAC) may progress to refractory, metastatic disease. We queried whether comprehensive genomic profiling (C...

4531Background: Using comprehensive genomic profiling (CGP), we queried whether FGFR3-driven mUCB could be further defined by additional genomic alterations (GA) and biomarkers of response to immun...

12092Background: Amplification (AMP) of PD-L1 (CD274/B7H1) has recently been linked to enhanced benefit from immune checkpoint inhibitor (ICPI) treatment. We used CGP to evaluate the PD-L1 GA lands...

e16530Background: Primary sarcomas of the urinary bladder (Bsarc) represent a rare but highly aggressive genitourinary malignancy. We searched for potential biomarkers for targeted and immunotherap...

4555Background: Although both seminomatous (Sem) and nonseminomatous (NS) TGCT have a favorable response to platinum-based chemotherapy (CT), a small proportion of them are chemorefractory. Therape...

e21629Background: Melanomas are heterogenous tumors that develop on many skin regions and harbor diverse genomic alterations (GA). Lesion subtypes are identifiable by location and/or genomic profil...

e14084Background: Choroid plexus tumors (CPT) include papilloma (CPP), atypical papilloma (ACPP) and carcinoma (CPC) types. We hypothesized that comprehensive genomic profiling (CGP) could uncover ...

552 Background: mPSCC is an aggressive malignancy with limited treatment options. Using CGP, we compared the therapy impacting genomic alterations (GA) between mPSCC and cutaneous mCSCC. Methods: DNA was extracted from 40 microns of FFPE samples from 78 cases of mPSCC and 338mCSCC.Comprehensive genomic profiling (CGP) was performed using a hybrid-capture, adaptor ligation based next generation sequencing assayto a mean coverage depth of > 500X. Tumor mutational burden (TMB) was determined on 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Results: mPSCC patients were younger than mCSCC (Table). Both tumors types feature high CDKN2A, TERT and FAT1 GA frequencies. NOTCH1 and PTCH1 GA are also more common in mCSCC than mPSCC. CD274 ( PD-L1) amplification was rare in both tumor types. Targeted therapy opportunities in mPSCC included alterations in kinase pathways ( EGFR GA in 6%; FGFR3 and ERBB2 GA in 4%); MTOR pathway ( NF1 GA in 7% and PTENGA in4%) and DNA repair pathway ( BRCA2and ATMGA in 7%). TMB was significantly higher in the UV light exposed mSCC than mPSCC with both tumor types having potential for responsiveness to immunotherapies. MSI-High status was extremely rare for both mPSCC and mCSCC. HPV viral DNA was identified in 29% on mPSCC but only in 5% of mCSCC. TP53 GA were significantly more frequent in HPV- than HPV+ mPSCC and mCSCC respectively (P < 0.0001 for both). Clinical outcomes of selected patients will be presented. Conclusions: mPSCC is a unique subtype of SCC with distinctive genomic features that contrast with those identified in mCSCC of non-penile UV light exposed skin. Given the potential opportunities for targeted therapies and immunotherapies that can be uncovered, continued study of CGP for the guidance of treatment for patients with mPSCC appears warranted.[Table: see text]

348 Background: We performed comprehensive genomic profiling (CGP) to learn whether sub-categorization of TMPRSS2 fusion status would impact therapy opportunities in patients with refractory CRPC and CRNEPC. Methods: DNA was extracted from 40 µm of FFPE sections of 2,424CRPC and 143 CRNEPC. CGP was performed on hybridization-captured, adaptor ligation-based libraries for up to 315 cancer-related genes. Tumor mutational burden (TMB) was determined on 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Results: The median ages for all 4 groups was similar (Table). TMPRSS2+( TMP+) CRPC features significantly greater TP53 and PTEN GA and TMPRSS2-( TMP-) CRPC featured higher MYC and ATM GA. Differences in BRCA2 and RB1 GA were not significant in the CRPC group. RB1 GA were more frequent in CRNEPC than CRPC. TP53 GA were higher in TMP+ CRNEPC than in TMP+ CRPC whereas GA in PTEN and MYC were similar in comparative groups. GA in AR and ATM were more frequent in CRPC than CRNEPC. The median TMB was higher in CRNEPC than CRPC and higher in TMP- than TMP+ tumors. TMP- CRPC and TMP- CRNEPC had higher TMB levelsthan TMP+ tumors in both groups. MSI-High status was more frequent in the TMP- CRPC and TMP- CRNEPC groups. Conclusions: For CRPC but not CRNEPC, the frequency of TMP+CRPC cases appears lower in advanced vsearly stage disease (TCGA data). CGP reveals significant differences in both targetable GA and markers of immunotherapy response between TMP+ and TMP- CRPC and CRNEC. Thus, when CRPC and CRNEPC areevaluated as to their TMPRSS2:ERG fusion status, significant genomic differences emerge which may impact therapy selection.[Table: see text]

640 Background: Collecting duct carcinoma (CDC) and renal medullary carcinoma (RMC) represent rare tumors that arise in the renal medulla are therapy resistant tumors that progress rapidly. Methods: DNA was extracted from 40 microns of FFPE specimen from refractory CDC (46 cases) and RMC (24 cases). CGPwas performed using a hybrid-capture, adaptor ligation based next generation sequencing assayto a mean coverage depth of > 800X. Tumor mutational burden (TMB) was calculated from a minimum of 1.11 Mb of sequenced DNA as previously described and reported as mutations/Mb. Microsatellite instability status (MSI) was determined on 114 loci. Results: All CDC patients were older and more frequently male (Table). Sickle cell trait was identified in both CDC and RMC, but far more frequently associated with RMC. All (100%) of CDC and RMC were clinically advanced Stage III and IV tumors with the primary tumor used for CGP in 70% of cases and a metastasis biopsy was sequenced in 30%. All (100%) CDC and RMC were intermediate (Grade 3) or high grade (Grade 4). In both tumor types, the GA/tumor was relatively low and there were no (0%) VHL GA. SMARCB1 GA were significantly more frequent in RMC than CDC but common in both tumors. Targeted therapies for kinase ( EGFR, RET) and MTOR ( NF2, TSC2) pathways were more frequent in CDC than RMC. At 1.8 mut/Mb, the median TMB was low for both tumor types with no (0%) of cases showing≥20 mut/Mb. No (0%) of the CDC or RMC cases featured MSI-high status. Conclusions: In addition to their histologic differences, the frequencies and types of GA seen in CDC differ significantly from that seen in RMC. The opportunities for biomarker driven targeted therapies for bothCDCand RMC appear limited with rare opportunities to target GA in TKGFR and MTOR pathways for CDC. Similarly, the relatively low TMB and absence of MSI-High status in CDC and RMCalso predicts that these tumors may be resistant to immunotherapies.[Table: see text]

565 Background: Although PSand NS testicular GCT have a favorable prognosis, on occasion these tumors can be refractory to conventional systemic treatments. Methods: FFPE tissues from 22 PS and 86 NSunderwent hybrid-capture based CGP to evaluate all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on 1.1 Mbp of sequenced DNA and reported as mutations (mut) per megabase (Mb) and microsatellite instability (MSI) was determined on 114 loci. Results: PS patients were older than NS (P=0.007). The primary tumor was sequenced in 41% of PS and 18% of NS with a metastasis sample in 59% of PS and 82% of NS.Four (18%) of PS had syncytial trophoblast cells identified. The mean GA frequency at 4.1 mut/case for NS was higher than that seen in PS and this difference reached near significance (P=0.08). The KRAS, TP53, CCND2 and FGF6/23 GA frequencies were similar in both tumor types (Table). GA in KIT, PIK3CA/ MTOR, PTEN and BRCA2 were more frequent in PS than NS whereas BRAF and ERBB2 GA were more frequent in NS (Table). MSI-High status was absent in in PS (0%) and identified in 2% of NS. Higher levels of TMB were not encountered in PS (0% TMB ≥10 mut/Mb), but higher TMB levels were more frequent in NS (5% ≥ 10 mut/B and 1% ≥ 20 mut/Mb). Conclusions: The GA found in refractory PS and NS differ significantly. PS features a lower GA frequency with slightly higher potential for targeted therapies in kinase (KIT) and MTOR pathways but, has very low TMB predicting limited opportunities for immunotherapy for these patients. For NS targeted therapy biomarkers appear even more uncommon than seen in PS with only extremely rare kinase inhibitor opportunities. However, based on rare high TMB and MSI-High status, immunotherapies may be of benefit in a small subset of NS patients. Further study of genomic findings in relapsed and clinically aggressive PS and NS appears warranted. [Table: see text]

1099 Background: A series of reports demonstrating the successful use of BRAF and MEK inhibitors in clinically advanced non-melanoma cancers has recently emerged. BRAF alterations in metastatic breast cancer (mBC) are rare and BRAF is not currently considered a target for the disease. Methods: DNA was extracted from 40 microns of FFPE sections from a series of 10,428 cases of metastatic breast cancer (mBC). Comprehensive genomic profiling (CGP) was performed on hybridization-captured, adaptor ligation based libraries to a mean coverage depth of > 550X for up to 315 cancer-related genes plus 37 introns from 14 genes frequently rearranged in cancer. Results: 135 (1.2%) of the mBC featured alterations in BRAF. The median age of the 135 female patients was 66 years (range 27 to 83 years). The primary tumor was used for CGP in 50 (37%) and from metastatic sites including lymph nodes, liver, bone, lung, brain, adrenal and soft tissue in 85 (67%). Using CDH1 mutation as the definition of lobular mBC, 126 (93%) were ductal and 9 (7%) were lobular histology. Activating BRAF alterations included amplifications (48%), SV mutations (39%) and rearrangements (13%). No (0%) mBC had multiple BRAF GA in the same case. 34% of BRAF SV were V600E and 66% were a wide variety of non-V600E GA. 10 (7.4%) of 135 BRAF mutated mBC featured ERBB2 amplification with 1 (1%) having an ERBB2 SV mutation and 1 (1%) having both ERBB2 amplification and SV GA. Of the 115 BRAF GA cases with known hormone receptor status 71 (62%) were ER negative, 44 (38%) were ER positive and 63 (55%) were triple negative (TNBC). Other targetable genes enriched in mBC with BRAF GA included CDK6 (p = 0.001), HGF (p < 0.001) and MET(p < 0.001). The median TMB was 4.5 with 17 (13%) of cases with TMB > 10 mut/Mb and 7 (5%) of cases with > 20 mut/Mb. Conclusions: BRAF alterations, although uncommon in mBC representing only 1.2% of cases, are enriched in TNBC and feature both targetable base substitutions and rare fusions. BRAF GA may be a rare cause of anti-HER2 therapy resistance in a subset of ERBB2 driven mBC. Targetable genes co-altered with BRAF in mBC include CDK6, HGF and MET. The TMB in BRAF altered mBC is significantly higher than that for mBC in general and indicates potential role for immunotherapy for these patients.

3583 Background: ERBB2 ( HER2) genomic alterations (GA) are evolving therapy taregets in metastatc coorectal cancer (mCRC). Methods: Hybrid capture based comprehensive genomic profiling (CGP) was performed on 8874 (9.6%) mCRC including both colonic adenocarcinomas (7587 cases; 85%) and rectal adenocarcinomas (1287 cases, 15%) Tumor mutational burden (TMB) was calculated from a minimum of 1.2 Mb of sequenced DNA. Results: ERBB2 amplifications or a short variant (SV) alterations or both were found in 433 (4.9%) of the total mCRC. 195 (45%) of the ERBB2 positive mCRC were female and 238 (55%) were male. Median age was 54 years (range 22 to 88 years). The most frequently co-altered genes were SV GA in TP53 (82%), APC (70%), KRAS (26%), SMAD4 (15%) and PIK3CA (13%). Clinically relevant GA significantly under-represented in ERBB2-altered CRC included significantly reduced GA in KRAS at 26% (p = 0.001) and BRAF at 4% (p = 0.003) as well as other kinases at 1% including EGFR, KIT, MET and RET. The frequency of TMB at > 10 mut/Mb (p < 0.0001), but at > 20 mut/Mb mCRC cases demonstrated virtually the same results regardless to ERBB2 status at a frequency of x%. The overall ERBB2 GA frequency at 5.3% in rectal mCRC is slightly higher than that seen in colonic mCRC at 4.9%, (p = 0.36). The frequency of TMB > 10 mut/Mb in ERBB2 WT mCRC is greater in the colonic mCRC than the rectal mCRC (p < 0.0001 for both comparisons). When > 20 mut/Mb is used as the cut-off, the greater frequency of TMB in colonic mCRC versus rectal mCRC remains significant (p < 0.0001). When the ERBB2altered mCRC cases are evaluated, the greater frequency of TMB > 10 mu/Mb in colonic mCRC versus rectal mCRC remains significant (p = 0.009), but the greater frequency in colonic verses rectal mCRC at the > 20 mut/Mb is not significant (p = 0.37). Conclusions: Although lower than observed in breast and upper gastrointestinal carcinomas where anti-HER2 therapies are approved indications, the frequency of ERBB2 GA in CRC at 4.9% is significant. Importantly, nearly half of CRC ERBB2 alterations are SVs, not detectable by routine IHC and FISH testing. However, the success of anti-HER2 therapies shown here and progress in on-going clinical trials indicates that targeting ERBB2 has potential to become an approved advance in precision therapy for mCRC patients.

11595 Background: Genomic fusions of the anaplastic lymphoma kinase gene ( ALK) are an established therapy target for patients with non-small cell lung cancer (NSCLC), but are not well-characterized in non-NSCLC malignancies. Methods: Comprehensive genomic profiling (CGP) of 92,784 clinically advanced malignancies was performed using a hybrid-capture, adaptor ligation based NGS assay to a mean coverage depth of >600X. Tumor mutational burden (TMB) was calculated from a minimum of 1.1 Mb of sequenced DNA. Results: 17,127/92,784 (18.5%) were NSCLC and 75,657 (81.5%) were non-NSCLC. Of the 697 (0.8%) of cases with ALK fusions, 554 (79%) were identified in NSCLC and 143 (21%) in non-NSCLC including 67 carcinomas; 39 sarcomas including 30 non-uterine and uterine leiomyosarcomas and inflammatory myofibroblastic tumors; 24 in hematolymphoid malignancies including non-Hodgkins lymphomas, myelomas and histiocytic malignancies; 3 in gliomas; 2 each in mesotheliomas, neuroblastomas and undifferentiated malignancies and 1 in melanoma. ALK fusions were significantly more frequently identified in NSCLC (3.2%) than in non-NSCLC (p

4076 Background: Gallbladder carcinoma (GBC) is commonly diagnosed at an advanced, unresectable disease stage and has a poor prognosis. Comprehensive genomic profiling (CGP) has a developing role in guiding systemic, precision anti-cancer therapy. Methods: We performed hybrid capture-based CGP on FFPE samples for 491 consecutive advanced GBCs. Mean coverage depth was >550X for up to 315 cancer-related genes plus 37 introns from 28 genes frequently rearranged in cancer. All 4 classes of genomic alterations (GA) were detected. Tumor mutational burden (TMB) was determined on up to 1.1 Mb of sequenced DNA. Results: Median age was 64 (range 25-88) and 69% (337/491) of patients were female. 96% (470), 2.9% (14), and 1.4% (7) of GBC patients had the diagnosis of adenocarcinoma, adenosquamous, or carcinoma not specified (NOS), respectively. Commonly altered genes were TP53 (62%), CDNK2A (31%), ARID1A (18%), and SMAD4 (15%), and most of the genetic aberrations (GA) were short variants. Potentially targetable SCNAs (including ERBB genes, MET, FGFRs, and the CCND1-FGF3/4/19 11q13 amplicon) were identified in 21% of cases (Table). Oncogenic BRAF, ALK, or FGFR2/3 rearrangements were found in 7 cases (1.4%). Moreover, 7.8% of cases had BRCA2 or ATM GA, and 0.8% had INI1loss suggesting benefit from PARP or EZH2 inhibitors, respectively. TMB was low; the 25th, 50th, and 75th percentiles were 2.5, 3.8 and 6.3 mutations/Mb, respectively. Less than 1% of cases had microsatellite instability. Radiological response to TKIs and immunotherapy was noted. Conclusions: In addition to the significant opportunity for anti-HER targeted therapies, other subsets of GBC cases harbored kinase GA (particularly SCNA), the 11q13 amplicon, or BRCA2/ ATM/ INI1mutations that are linked to therapeutic benefit. How the frequency of both driver SCNA and DNA repair alterations in GBC can be linked with inflammation awaits additional investigation. [Table: see text]

9072 Background: Although far less common than BRAF V600E base substitutions (subs) classically associated with melanomas and colorectal carcinomas, BRAF subs occur in 1-2% of non-small cell lung cancer (NSCLC). BRAF fusions are emerging treatment targets for Spitzoid melanomas and other solid tumors. The frequency of BRAF fusions and targeting potential in NSCLC has not been widely described. Methods: Hybridization capture-based comprehensive genomic profiling (CGP) was performed on 17,128 NSCLC FFPE samples sequenced to a mean coverage depth of > 550X for up to 315 cancer-related genes plus 37 introns from 19 genes frequently rearranged in cancer. Genomic alterations (GA) included short variant (SV) base subs and insertions/deletions, copy number alterations, and rearrangements/fusions. Tumor mutational burden (TMB; mut/Mb) was calculated on up to 1.1 Mb of sequenced DNA. Results: BRAF fusions were identified in 42/17,128 (0.2%) NSCLC profiled. Median patient age was 67 (range 44-93 yrs). Of the BRAF fusion positive NSCLC, 55% were female. Biopsies were obtained from primary lung tumor (48%) and metastatic sites (52%). The most frequent 5’ partners were AGK, DOCK4, and TRIM24. Multiple novel BRAF fusions were identified. The genes most frequently co-altered with BRAF fusions were TP53(67%), CDKN2A(31%), EGFR (29%) and CDKN2B (26%). Overall TMB in the BRAFfusion positive cohort was low (median 3.8 mut/Mb), although 3/42 cases (7%) had > 20 mut/Mb. Of the BRAF fusion driven NSCLC, 10 cases (24%) featured EGFR SV alterations. Two BRAF fusion/ EGFR SV cases featured primary exon 19 deletion and T790M mutation. Examples of BRAF fusion driven NSCLC responding to a combination of BRAFand MEK inhibitors (MEKi) will be presented. Conclusions: NSCLC BRAF fusions are a rare GA that may be associated with acquired resistance in a subset of EGFR-mutated NSCLC progressing on anti- EGFR TKI therapies. Given clinical evidence for the activity of targeted therapy approaches, molecular eligibility for clinical trials of MEKi should include these variants. The clinical evidence for responsiveness of BRAF fusion driven NSCLC provides an opportunity to personalize treatments and improve clinical outcomes for patients.

1016 Background: Clonal evolution during progression to and treatment of mBC highlights the importance of genomic profiling of recent samples to guide clinical decision making. We undertook this study to characterize genomic alterations (GA) in ctDNA from pts with mBC during the course of clinical care. Methods: Hybrid-capture based genomic profiling of 62 genes (FoundationACT) was performed on ctDNA from 255 BC pts. The fraction of ctDNA in the blood was estimated using the maximum somatic allele frequency (MSAF) for each sample. Results: 168 pts were ER+ [16 HER2+, 134 HER2(-), 18 HER2 unknown (unk)]; 51 were ER(-) [7 HER2+, 38 triple negative (TNBC), 6 HER2 unk]; 36 were ER unk; 95% were stage 4. For pts with treatment information, 90% had prior chemotherapy and 90% ER+ pts had prior aromatase inhibitor therapy (AI). ≥1 GA was reported in 78% of all cases and in 88% of cases with evidence of ctDNA in the blood (MSAF >0). For 226 cases with MSAF >0, an average of 2.7 GA/case were reported. The most common GA for ER+ pts were in TP53 (44%), PIK3CA (39%), ESR1 (36%), CDH1 (11%), KRAS (10%) and ERBB2 ( HER2, 9%). 101 ESR1 GA were identified in 61 pts [54 ER+, 7 ER unk], including 4 HER2+ pts. For ER+ pts with treatment information: 37% (22/60) with prior AI had ESR1 GA; all pts with ESR1 GA had prior AI. 24 pts had >1 ESR1 GA, with instances of GA in cis. Frequent ESR1 GA were Y537S/N (n=47), D538G (n=29) and E380Q (n=7); rearrangement (n=3) and amplification (n=1) were also detected. Concurrent GA with ESR1 were found in PIK3CA (41%), FGFR1 (13%), BRCA1/2 (5%), HER2 (5%) and AKT1 (3%). In ER(-) pts, the most common GA were in TP53 (74%), PIK3CA (17%), NF1 (11%), BRCA1 (9%) and EGFR (9%). HER2 activating mutation occurred in 3% of cases that were HER2(-) by prior testing. Kinase fusions in FGFR2/3 (3 ER+) and EGFR (1 TNBC) were observed. Conclusions: In this study, evidence of ctDNA in the blood was observed in 89% of cases. PIK3CA and ESR1 GA frequencies were similar to those reported in previous studies of ctDNA from ER+ pts after AI. Diverse ESR1 GA and co-occurring GA suggest therapeutic approaches for AI refractory ER+ mBC. Our results demonstrate that genomic profiling of ctDNA may be a complementary approach to tissue-based genomic testing for pts with mBC.

11512 Background: Primary squamous cell carcinomas (SCCs) have diverse etiologies, but can share genomic features. We reviewed the genomic profiles of a series of SCC cases of differing anatomic origin. Methods: Hybrid-capture based genomic profiling of 182 or 236 or 315 genes was performed on 4783 squamous malignancies in the course of clinical care, with baits for HPV6, 11, 16, and 18, and assessment of tumor mutation burden (TMB; mutations/Mb) and microsatellite instability. Results: Sites of origin were head and neck (HNSCC, n = 1300), cervical (cSCC; n = 318), anal (aSCC, n = 248), esophageal (n = 242), lung (lSCC, n = 2386), and cutaneous (sSCC, n = 289) SCC cases. For HNSCC, cSCC, and aSCC (collectively termed HCA SCC), 395 (30%), 215 (68%), and 211 (83%) were HPV positive, respectively. For HCA SCC, the most common GA were in TP53 (45%), CDKN2A (29%), PIK3CA (24%), TERT (21%), and FAT1 (14%). The most frequent GA differentially associated with HPV status were in PIK3CA (34.9% versus 16.0%), CYLD (11.4% versus 1.4%) and PTEN (14.8% versus 6.1%) for HPV+ cases, and TP53 (3.8% versus 76.5%), CDKN2A ()1.4% versus 49.8%), and TERT (4.3% versus 33.0%) for HPV- cases. Mean TMB for HPV+ and HPV- cases were 6.6 (STDEV 7.3) and 13.7 (STDEV 29.7), respectively. TMB of all SCC cases was significantly different (p < 10-12) when stratified by HPV status. For lSCC and eSCC, the most common GA were found in TP53 (86%) CDKN2A (40%), and PIK3CA (26%) and mean TMB was 11.6 with HPV found in 3.1% of cases. In sSCC, the most common GA were in TP53 (85.5%), CDKN2A (54.3%), and TERT(44.0%), and mean TMB was 59.5 with HPV in 3.1% of cases. Subsets of SCC cases had defining and targetable GA including bi-allelic deletion of SMARCB1 ( < 0.3%), amplification of PD-L1 (~2% ), and various kinase fusions. Cases demonstrating radiologic response to immunotherapy and matched targeted therapies, as well as subsequent development of multiple mechanisms of acquired resistance, will be presented. Conclusions: HPV driven SCC have similar genomic profiles regardless of of site origin, and have a significantly lower median TMB than HPV negative SCC. Early consistency of responses of SCC to matched therapies may strengthen the case for site independent genomic predictors of therapy response.

e13031 Background: In Cutaneous Squamous Cell Carcinoma (cSqCC), Notch1, Notch2, and Notch3 have been identified as tumor suppressors with a high rate of inactivating mutations early in cSqCC pathogenesis. Despite the high frequency of alterations, the biologic and therapeutic implications of Notch genomic alterations (GAs) in cSqCC are incompletely understood. Methods: 232 FFPE samples of cSqCC were evaluated by comprehensive genomic profiling (CGP) of 315 genes and analyzed for all classes of GAs, with diagnoses confirmed by central pathology review. Notch GAs with unknown functional impact were excluded. Tumor mutational burden (TMB) was calculated from 1.11 Mb of sequenced DNA and reported as mutations/Mb. Results: The cohort of 232 samples was 78% male and 22% female, aged from 17 to 88, with confirmed metastatic disease in 32% of cases. 115 (50%) samples had a Notch family member GA with a known or predicted functional impact. 96 cases had Notch1 GAs, 43 cases had Notch2 GAs, and 14 cases had Notch3 GAs with 40 cases having GAs in multiple Notch family members. These mutations were 41% missense, 34% nonsense, 15% splice site, 9% frameshift indels, and 1% non-frameshift indels alterations. Patients with Notch GAs were significantly older (median 70 years old vs median 64, p < 0.01). TMB was increased among samples with Notch GAs (median TMB of 63 mutations/mb versus 20 mutations/mb, p < 1x10-6), with similar differences for primary and metastatic samples. Cases with Notch GAs had more total GAs per case (mean 10.4 vs 7.4, p < 1.5x10-10); however, the top co-mutated genes were the same (TP53, CDKN2A, FAT1, MLL2). Both groups had a high proportion of C- > T/G- > A transitions, consistent with UV damage; however, the proportion was higher in cases with Notch GAs (median 83% vs 80%) - a difference seen in primary and metastatic samples. Conclusions: 50% of cSqCC cases had a Notch family member loss of function GA, which was associated with increased TMB in the primary and metastatic setting. With pre-clinical models and case studies showing responses to PD-1 inhibitors in cSqCC, further investigations are warranted into the associations of Notch GAs with mutational burden and response to immunotherapy.

9536 Background: MM is a highly targetable malignancy, with both kinase inhibitors and immunotherapies providing meaningful survival benefit. Different subtypes of mm harbor distinct GA that suggest targeted and immunotherapy options. Methods: Comprehensive genomic profiling was performed in 2,197 MMs for up to 315 cancer-related genes plus introns from 28 genes commonly rearranged in cancer on hybrid-capture, adaptor ligation-based libraries (mean coverage depth > 600X). TMB was calculated from ≥1.11 Mb sequenced DNA. We assessed base substitutions, insertions and deletions (short variants; SV), rearrangements, and copy number changes. Results: We assessed 6 subtypes: routine cutaneous (CT; 90%), desmoplastic (DM: 1%), acral lentiginous (AL; 1%), Spitzoid (SP; 1%), mucosal (MC; 2%) and ocular (OC; 5%). Each group harbored characteristic genomic signatures (Table). BRAFwas mutated in 38% of CT of which 92% were SV GA and 8% were amplifications, fusions or cases with > 1 BRAF GA. High TMB in CT and DM is highly prevalent (42% and 83% with > 20 mut/Mb). BRAFGA were less common in AL (18%), MC (15%), and OC (2%). SP GA were dominated by fusions in BRAF (60%) and other kinases. KIT GA were prominent in MC and AL. TMB for MC and OC mm were very low. Key findings include novel drivers of BRAF inhibitor resistance including BRAFinternal rearrangements and kinase domain duplications. Conclusions: In the largest cohort of mm with NGS to date, genomic profiles and TMB differ across mm subtypes. Highly prevalent BRAF GA (including in the SP variant) and high TMB in CT and DM mm permit effective use of targeted and immunotherapies. Although MC and OC have lower BRAF GA frequency and lower TMB, targetable GA can be present. Novel BRAF inhibitor resistance mechanisms were observed. [Table: see text]

429 Background: Relapsed and refractory urethral cancer (UrethC) is a rare form of genito-urinary malignancy that includes urothelial carcinoma (UC), squamous cell carcinoma (SCC), adenocarcinoma (AC) and clear cell carcinoma (CCC) subtypes. No standard treatment exists. Methods: DNA was extracted from 40 microns of FFPE specimen from 46 cases of mUrethC. Comprehensive genomic profiling (CGP) was performed using a hybrid-capture, adaptor ligation based next generation sequencing assay to a mean coverage depth of >500X. Tumor mutational burden (TMB) was calculated from a minimum of 1.11 Mb of sequenced DNA as previously described and reported as mutations/Mb. The results were analyzed for all classes of genomic alterations (GA), including base substitutions, insertions and deletions (short variants; SV), fusions, and copy number changes including amplifications (amp) and homozygous deletions. Results: The clinical features, GA, TMB findings in the mUrethC patients and the subtypes of UrethC are shown in the Table. In comparison with 1,183 similarly profiled UC of the bladder (UCB), all 46 mUrethC and the 21 urothelial mUrethC as a separate group widely differed in GA frequencies. With the exception of similar TP53 GA frequencies, there were significantly lower GA in ERBB2, FGFR1-3 and PIK3CAin the mUrethC cases (p 20 mut/Mb (4%; p=0.0001). Conclusions: CGP of mUrethC reveals distinctive genomic alteration frequencies among the 4 disease subtypes with higher numbers of GA in the AC than in the UC, SCC and CCC. The TMB appears to be lower in mUrethC than classically seen in UCB where checkpoint inhibition is now approved. Further study of this rare form of genitourinary cancer appears warranted. [Table: see text]

350 Background: Small cell neuroendocrine carcinoma of the bladder (SCCB) is rare but aggressive form of genitourinary cancer that can arise de novo or in conjunction with urothelial carcinoma (UCB). Methods: DNA was extracted from 40 microns of FFPE specimen from 29 cases of relapsed, refractory and metastatic SCCB and 1,113 UCB. Comprehensive genomic profiling (CGP) was performed using a hybrid-capture, adaptor ligation based next generation sequencing assay to a mean coverage depth of > 503X. Tumor mutational burden (TMB) was calculated from a minimum of 1.11 Mb of sequenced DNA as previously described and reported as mutations/Mb. The results were analyzed for all classes of genomic alterations (GA), including base substitutions, insertions and deletions (short variants; SV), fusions, and copy number changes including amplifications (amp) and homozygous deletions. Results: 29 SCCB cases were confirmed on routine histology and featured positive IHC staining for chromogranin, synaptophysin or both. Patients had a mean age of 68.1 years (range 49-90 years) and 25 (86%) were male. At the time of CGP, 3 (10%) SCCB were Stage III and 26 (90%) were stage IV. The primary SCCB was used for sequencing in 14 (48%) of cases and a metastasis sample in 15 (52%). The 29 SCCB featured 2.86 GA/case.The genomics of SCCB differed significantly from UCB (Table). The most frequent clinically relevant GA in SCCB were RICTOR amp (21%) and PIK3CA (10%), BRCA1, HGF, FBXW7 and CCND2 SV (7% each). The relatively high TMB in SCCB (7% TMB > 20 mut/Mb and 28% TMB > 10 mut/Mb) is similar to that seen in UCB. No SCCB cases were MSI-high. ERBB2 and FGFR1 GA frequencies (both 3%) in SCCB were lower than in similarly studied UCB. Conclusions: SCCB differs in genomic landscape from UCB in having higher frequencies of TP53 and RB1 GA and lower frequencies of FGFR3 and ERBB2 GA. However, like UCB, SCCB shares the presence of multiple GA associated with potential responses to targeted therapies and high TMB associated with response to immune checkpoint inhibitor therapy. [Table: see text]

282 Background: Large scale, retrospective, sequencing projects have identified well-defined subtypes of PDAC, but therapeutic paradigms remain unchanged. We hypothesized that genomic alterations associated with PDAC in young adults (YA, age < 50) are distinctly different from that of older adults (OA, age > 50) to identify an enrichment of targetable alterations. Methods: DNA was extracted from formalin fixed paraffin embedded (FFPE) PDAC clinical specimens and comprehensive genomic profiling (CGP) was performed on hybrid-capture, adaptor ligation based libraries to a mean coverage depth of > 600 for up to 315 genes plus 47 introns from 19 genes frequently rearranged in cancer. Results: CGP was performed on 1533 FFPE PDAC specimens, 566 (36.9%) were from the primary tumor, 967 (63.1%) from metastatic sites. Median age at diagnosis was 63 years (yrs), 180 (11.7%) were YA. KRAS mutations were identified in 78.7 of YA and 87.7% of OA. The differentially altered genes between the two groups were KRAS (p = 0.004), TP53 (p = 0.04), BRCA2 (p = 0.02), AKT2 (p = 0.03), MAP2K4 (P = 0.003) and DNMT3A (p = 0.0002). The median tumor mutational burden (TMB) for the entire study set was 2.7 (YA – 2.5, OA –2.7). BRAF kinase domain deletion was observed in 1 patient (OA). ALK fusions were present in 2 patients (1 YA & 1 OA) and these patients had durable responses to specific ALK inhibitors. Conclusions: The majority of the genomic alterations identified were not significantly different on the basis of age. However, identification of subpopulations, such as ALK kinase fusions and BRAF kinase domain deletions that can translate into sustained clinical benefit from matched targeted therapy is promising. This underscores the importance of CGP in PDAC to investigate other targetable genomic alterations.

5591Background: IO holds promise for EA with mismatch repair (MMR) or MSI-H phenotype, while trials of targeted agents matched by histology/single biomarkers have yet to meet clinical endpoints. We...

9522Background: Although cutaneous cBCC and cSCC are the most frequent primary human cancers, primary treatment is nearly always curative, and metastatic disease (mcBCC and mcSCC) rarely develops. ...