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Ritanserin inhibits macropinocytosis and acidic organelle homeostasis in TSC2-deficient cells

Lymphangioleiomyomatosis is a rare destructive lung disease affecting primarily women and is the primary lung manifestation of tuberous sclerosis complex (TSC). In lymphangioleiomyomatosis, biallelic loss of TSC1/2 leads to hyperactivation of mTORC1 and inhibition of autophagy. To determine how the metabolic vulnerabilities of TSC2-deficient cells can be targeted, we performed a high-throughput screen utilizing the “Repurposing” library at the Broad Institute of MIT and Harvard (Cambridge, MA), with or without the autophagy inhibitor chloroquine. Ritanserin, an inhibitor of diacylglycerol kinase alpha (DGKA), was identified as a selective inhibitor of proliferation of Tsc2−/− mouse embryonic fibroblasts (MEF), with no impact on Tsc2+/+ MEFs. DGKA is a lipid kinase that metabolizes diacylglycerol to phosphatidic acid, a key component of plasma membranes. Phosphatidic acid levels were increased 5-fold in Tsc2−/− MEFs compared with Tsc2+/+ MEFs, and treatment of Tsc2−/− MEFs with ritanserin led to depletion of phosphatidic acid as well as rewiring of phospholipid metabolism. Macropinocytosis is known to be upregulated in TSC2-deficient cells. Ritanserin decreased macropinocytic uptake of albumin, limited the number of lysosomes, and reduced lysosomal activity in Tsc2−/− MEFs. In a mouse model of TSC, ritanserin treatment decreased cyst frequency and volume, and in a mouse model of lymphangioleiomyomatosis, genetic downregulation of DGKA prevented alveolar destruction and airspace enlargement. Collectively, these data indicate that DGKA supports macropinocytosis in TSC2-deficient cells to maintain phospholipid homeostasis and promote proliferation. Targeting macropinocytosis with ritanserin may represent a novel therapeutic approach for the treatment of TSC and lymphangioleiomyomatosis.Significance:This study identifies macropinocytosis and phospholipid metabolism as novel mechanisms of metabolic homeostasis in mTORC1-hyperactive cells and suggest ritanserin as a novel therapeutic strategy for use in mTORC1-hyperactive tumors, including pancreatic cancer.

Enfortumab Vedotin (EV) is approved for metastatic urothelial carcinoma (mUC) progressing post-platinum and PD1/L1 inhibitor therapy. Erdafitinib is approved for post-platinum mUC with activating somatic genomic alterations (GAs) in FGFR2/3. Information on the activity of EV in mUC with FGFR2/3 alterations will facilitate optimal clinical management. In this multi-center, retrospective analysis, we assessed the overall survival (OS), progression-free survival (PFS) and objective response rate (ORR) to EV in mUC patients with and without FGFR2/3 GAs including mutations and fusions. Multivariable cox-regression and logistic regression analyses with 2-tailed p-values were used to evaluate the association of GAs with outcomes. A majority of the evaluable 60 patients were male (44/60, 78%), exhibited ECOG performance score 0–1 (53/60, 88.3%) and had a median age of 70.5 (range 48 – 88) years when starting EV. GAs in FGFR2/3 did not influence the ORR (p=0.32), OS (p=0.79) or PFS (p = 0.32) with EV. In conclusion, FGFR2/3 GAs did not appear to compromise major outcomes with EV in mUC. Larger studies are required to further evaluate the impact of FGFR2/3 GAs on the activity of EV and the optimal sequencing of EV and erdafitinib in mUC.

Background and aims CDH1 germline variants have been linked to heritability in diffuse gastric (DGC) and lobular breast cancer (LBC). Studies have not yet assessed whether CDH1 is a cancer-susceptibility gene in other cancers. Herein, we mapped the landscape of pathogenic and likely pathogenic (P/LP) germline variants in CDH1 across various cancers and ethnicities. Methods We evaluated CDH1 germline P/LP variants in 212,944 patients at one CLIA-certified laboratory (Invitae) and described their frequency in 7 cancer types. We screened for CDH1 variant enrichment in each cancer relative to a cancer-free population from The Genome Aggregation Database version 3 (gnomADv3). Results CDH1 P/LP variants were identified in 141 patients, most commonly in patients with DGC (27/408, 6.6%) followed by colorectal signet-ring cell cancer (CSRCC; 3/79, 3.8%), gastric cancer (56/2756, 2%), and LBC (22/6809, 0.3%). CDH1 P/LP variants were enriched in specific ethnic populations with breast cancer, gastric cancer, CRC, LBC, DGC, and CSRCC compared to matched ethnicities from gnomADv3. Conclusion We report for the first time the prevalence of P/LP CDH1 variants across several cancers and show significant enrichment in CDH1 P/LP variants for patients with CSRCC, DGC, and LBC across various ethnicities. Future prospective studies are warranted to validate these findings.

Purpose: Immune checkpoint inhibitors (ICI) have shown clinical benefit in many types of metastatic cancers with only a few predictive biomarkers identified so far. CDKN2A is commonly altered in human cancers, but prior studies have provided conflicting evidence regarding the association between CDKN2A genomic alterations (GA) and response to ICIs. Herein, we examined the impact of loss-of-function CDKN2A alterations on response and survival in patients treated with ICIs. Experimental Design: We studied the association between loss-of-function CDKN2A alterations and the response to ICIs in two independent cohorts of six different cancer types. Seven hundred and eighty-nine patients treated at Dana-Farber Cancer Institute (DFCI; Boston, MA) and 1,250 patients treated at Memorial Sloan Kettering Cancer Center (MSKCC; New York, NY) were included in the final analysis. Patients' tumors were sequenced using Oncopanel or MSK-IMPACT. RNA sequencing data from The Cancer Genome Atlas and IMvigor210 were used to investigate differences in the tumor microenvironment. Results: In the DFCI cohort, CDKN2A GAs were associated with poor response and survival in patients with urothelial carcinoma treated with ICIs, but not those treated with platinum-based therapy. Similarly, CDKN2A GAs were associated with worse outcomes in the MSKCC urothelial carcinoma cohort treated with ICIs. There was no association of CDKN2A status with ICI treatment outcome in five other cancers: esophagogastric, head and neck, non–small cell lung, renal cell carcinoma, and melanoma. Immuno-inflammatory pathways were significantly reduced in expression in CDKN2A-altered tumors. Conclusions: Our data show that CDKN2A GAs were associated with reduced benefit from ICI therapy in urothelial carcinoma as well as changes in the tumor–immune microenvironment.

Lymphangioleiomyomatosis is a rare destructive lung disease affecting primarily women and is the primary lung manifestation of tuberous sclerosis complex (TSC). In lymphangioleiomyomatosis, biallelic loss of TSC1/2 leads to hyperactivation of mTORC1 and inhibition of autophagy. To determine how the metabolic vulnerabilities of TSC2-deficient cells can be targeted, we performed a high-throughput screen utilizing the “Repurposing” library at the Broad Institute of MIT and Harvard (Cambridge, MA), with or without the autophagy inhibitor chloroquine. Ritanserin, an inhibitor of diacylglycerol kinase alpha (DGKA), was identified as a selective inhibitor of proliferation of Tsc2−/− mouse embryonic fibroblasts (MEF), with no impact on Tsc2+/+ MEFs. DGKA is a lipid kinase that metabolizes diacylglycerol to phosphatidic acid, a key component of plasma membranes. Phosphatidic acid levels were increased 5-fold in Tsc2−/− MEFs compared with Tsc2+/+ MEFs, and treatment of Tsc2−/− MEFs with ritanserin led to depletion of phosphatidic acid as well as rewiring of phospholipid metabolism. Macropinocytosis is known to be upregulated in TSC2-deficient cells. Ritanserin decreased macropinocytic uptake of albumin, limited the number of lysosomes, and reduced lysosomal activity in Tsc2−/− MEFs. In a mouse model of TSC, ritanserin treatment decreased cyst frequency and volume, and in a mouse model of lymphangioleiomyomatosis, genetic downregulation of DGKA prevented alveolar destruction and airspace enlargement. Collectively, these data indicate that DGKA supports macropinocytosis in TSC2-deficient cells to maintain phospholipid homeostasis and promote proliferation. Targeting macropinocytosis with ritanserin may represent a novel therapeutic approach for the treatment of TSC and lymphangioleiomyomatosis. Significance: This study identifies macropinocytosis and phospholipid metabolism as novel mechanisms of metabolic homeostasis in mTORC1-hyperactive cells and suggest ritanserin as a novel therapeutic strategy for use in mTORC1-hyperactive tumors, including pancreatic cancer.

The immune checkpoint inhibitor (ICI) pembrolizumab is US FDA approved for treatment of solid tumors with high tumor mutational burden (TMB-high; ≥10 variants/Mb). However, the extent to which TMB-high generalizes as an accurate biomarker in diverse patient populations is largely unknown. Using two clinical cohorts, we investigated the interplay between genetic ancestry, TMB, and tumor-only versus tumor-normal paired sequencing in solid tumors. TMB estimates from tumor-only panels substantially overclassified individuals into the clinically important TMB-high group due to germline contamination, and this bias was particularly pronounced in patients with Asian/African ancestry. Among patients with non-small cell lung cancer treated with ICIs, those misclassified as TMB-high from tumor-only panels did not associate with improved outcomes. TMB-high was significantly associated with improved outcomes only in European ancestries and merits validation in non-European ancestry populations. Ancestry-aware tumor-only TMB calibration and ancestry-diverse biomarker studies are critical to ensure that existing disparities are not exacerbated in precision medicine.

Tuberous Sclerosis Complex (TSC) is caused by TSC1 or TSC2 mutations, resulting in hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1). Transcription factor EB (TFEB), a master regulator of lysosome biogenesis, is negatively regulated by mTORC1 through a RAG GTPase-dependent phosphorylation. Here we show that lysosomal biogenesis is increased in TSC-associated renal tumors, pulmonary lymphangioleiomyomatosis, kidneys from Tsc2+/− mice, and TSC1/2-deficient cells via a TFEB-dependent mechanism. Interestingly, in TSC1/2-deficient cells, TFEB is hypo-phosphorylated at mTORC1-dependent sites, indicating that mTORC1 is unable to phosphorylate TFEB in the absence of the TSC1/2 complex. Importantly, overexpression of folliculin (FLCN), a GTPase activating protein for RAGC, increases TFEB phosphorylation at the mTORC1 sites in TSC2-deficient cells. Overexpression of constitutively active RAGC is sufficient to relocalize TFEB to the cytoplasm. These findings establish the TSC proteins as critical regulators of lysosomal biogenesis via TFEB and RAGC and identify TFEB as a driver of the proliferation of TSC2-deficient cells., Tuberous sclerosis complex (TSC) is a multiorgan disease that can lead to hyperactive mTORC1 due to deficient TSC1 or TSC2 protein function. Here, the authors find that despite high mTORC1 activity, TFEB localizes to the nucleus and drives lysosomal gene expression via a non-canonical Rag-dependent mechanism.

Germline studies in testicular cancer have focused on unselected populations but so far have not led to recommendations for testicular cancer screening.Herein, we hypothesized that men with testicular cancer and an additional risk factor for hereditary cancer predisposition carry a higher rate of pathogenic variants than men with testicular cancer without another risk factor.187 patients with a personal history of testicular cancer underwent germline testing via Invitae. Patients were divided into low-risk and high-risk patients. Low-risk patients (n=83) had testicular cancer as their only primary malignancy without a family history of testicular cancer. High-risk patients (n=104) had additional primary malignancies and/or a family history of testicular cancer. 23.1% of patients harbored pathogenic germline variants with 19.6% carrying actionable variants. Among low-risk patients, 13.5% carried pathogenic variants versus 29.9% in the high-risk cohort. Of patients with a family history of non-testicular cancers and a personal history of additional primary malignancies, 32% harbored pathogenic variants.High-risk patients are twice as likely to harbor pathogenic variants compared to low-risk patients. Importantly, patients with a family history of cancer and other primary malignancies represent a subset of patients that may benefit from genetic evaluation.

Summary: Prior studies of the renal cell carcinoma (RCC) germline landscape investigated predominantly patients of European ancestry. We examine the frequency of germline pathogenic and likely pathogenic (P/LP) variants in 1,829 patients with RCC from various ancestries. Overall, P/LP variants are found in 17% of patients, among whom 10.3% harbor one or more clinically actionable variants with potential preventive or therapeutic utility. Patients of African ancestry with RCC harbor significantly more P/LP variants in FH compared to patients of non-African ancestry with RCC and African controls from the Genome Aggregation Database (gnomAD). Patients of non-African ancestry have significantly more P/LP variants in CHEK2 compared to patients of African ancestry with RCC and non-Finnish Europeans controls. Non-Africans with RCC have more actionable variants compared to Africans with RCC. This work helps understand the underlying biological differences in RCC between Africans and non-Africans and paves the way to more comprehensive genomic characterization of underrepresented populations.

Background Academics in all disciplines increasingly use social media to share their publications on the internet, reaching out to different audiences. In the last few years, specific indicators of social media impact have been developed (eg, Altmetrics), to complement traditional bibliometric indicators (eg, citation count and h-index). In health research, it is unclear whether social media impact also translates into research impact. Objective The primary aim of this study was to systematically review the literature on the impact of using social media on the dissemination of health research. The secondary aim was to assess the correlation between Altmetrics and traditional citation-based metrics. Methods We conducted a systematic review to identify studies that evaluated the use of social media to disseminate research published in health-related journals. We specifically looked at studies that described experimental or correlational studies linking the use of social media with outcomes related to bibliometrics. We searched the Medical Literature Analysis and Retrieval System Online (MEDLINE), Excerpta Medica dataBASE (EMBASE), and Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases using a predefined search strategy (International Prospective Register of Systematic Reviews: CRD42017057709). We conducted independent and duplicate study selection and data extraction. Given the heterogeneity of the included studies, we summarized the findings through a narrative synthesis. Results Of a total of 18,624 retrieved citations, we included 51 studies: 7 (14%) impact studies (answering the primary aim) and 44 (86%) correlational studies (answering the secondary aim). Impact studies reported mixed results with several limitations, including the use of interventions of inappropriately low intensity and short duration. The majority of correlational studies suggested a positive association between traditional bibliometrics and social media metrics (eg, number of mentions) in health research. Conclusions We have identified suggestive yet inconclusive evidence on the impact of using social media to increase the number of citations in health research. Further studies with better design are needed to assess the causal link between social media impact and bibliometrics.

Background Since the beginning of the coronavirus disease 2019 (COVID-19) epidemic, misinformation has been spreading uninhibited over traditional and social media at a rapid pace. We sought to analyze the magnitude of misinformation that is being spread on Twitter (Twitter, Inc., San Francisco, CA) regarding the coronavirus epidemic. Materials and methods We conducted a search on Twitter using 14 different trending hashtags and keywords related to the COVID-19 epidemic. We then summarized and assessed individual tweets for misinformation in comparison to verified and peer-reviewed resources. Descriptive statistics were used to compare terms and hashtags, and to identify individual tweets and account characteristics. Results The study included 673 tweets. Most tweets were posted by informal individuals/groups (66%), and 129 (19.2%) belonged to verified Twitter accounts. The majority of included tweets contained serious content (91.2%); 548 tweets (81.4%) included genuine information pertaining to the COVID-19 epidemic. Around 70% of the tweets tackled medical/public health information, while the others were pertaining to sociopolitical and financial factors. In total, 153 tweets (24.8%) included misinformation, and 107 (17.4%) included unverifiable information regarding the COVID-19 epidemic. The rate of misinformation was higher among informal individual/group accounts (33.8%, p

Prior studies of the germline landscape of renal cell carcinoma (RCC) have centered around predominantly white patients of European ancestry. We examined the frequency of germline pathogenic and likely pathogenic (P/LP) variants in 1,829 patients with RCC from various ancestries. Overall, P/LP variants were found in 17%, among which 10.3% harbored ≥1 clinically actionable germline variant with potential preventive or therapeutic utility. Patients with African ancestry harbored significantly more P/LP variants in FH compared to patients of European ancestry. Patients with European ancestry had significantly more P/LP variants in CHEK2 and overall had more actionable variants compared to patients with African ancestry. This work helps better understand the underlying biological differences in RCC between Africans and Europeans. In addition, this work may pave the way to a much more comprehensive and global genomic characterization of underrepresented populations.

8559 Background: Malignnant mesothelioma (MM) is a highly lethal tumor that can develop in the pleura, the peritoneum, the pericardium or the testes. While the genomic features of pleural MM have been well-described overall, less is known about the distribution of genetic alterations (GAs) according to histology. In addition, few reports comparing genetic features according to disease site are available. Methods: We identified patients with pleural or peritoneal mesothelioma with mutational analysis through the GENIE registry. Patient tumor genetic data were provided by Memorial Sloan-Kettering Cancer Center (MSK)-IMPACT and Dana-Farber Cancer Institute (DFCI)-Oncopanel NGS initiatives. Patients with more than one sequenced sample were excluded. We limited our analysis to genes common to all versions of both panels and that were significantly mutated in the TCGA mesothelioma cohort. Mutation and copy number variant (CNV), collectively called GAs, were determined, and were compared using the Fisher’s Exact test and Kruskal-Wallis Test. Comparisons were made both by disease site (pleural vs. peritoneal) and histology for the pleural samples (epithelioid vs. biphasic vs. sarcomatoid). Nominal p-values were obtained, and FDR correction was employed (q

1559 Background: Tumor mutational burden (TMB), has been recently granted FDA approval as a biomarker for ICI treatment in tumors with a high mutation load (≥ 10/MB). To leverage this biomarker in the clinical setting, it is necessary to evaluate its application in diverse patient populations. In particular, tumor-only sequencing may overestimate TMB in non-EUR populations for which reference panels are small or unavailable, and thus have poorer predictive performance. Herein, we investigate the effect of TMB overestimation in non-EURs on patient diagnosis and clinical outcomes in a real world patient cohort. Methods: TMB was computed using a tumor-only NGS platform (Oncopanel) for 8349 cancer patients (pts) of 7 cancer types (Table). Genetic ancestry was inferred directly from tumor sequencing data and confirmed for a subset of pts using germline SNP arrays. TMB was compared using Wilcoxon rank-sum test between European (EUR) and non-EUR pts. TMB percentile rank by ancestral group (East Asian, African, European) and tumor histology was computed. In non-EUR pts, TMB was calibrated by reassigning its value to the corresponding percentile rank in EUR pts having the same cancer (AH-TMB). Tumors with raw TMB ≥ 10/MB were assigned as TMB-high (TMBH; with the rest referred to as TMBL for TMB-low) and those with calibrated AH-TMB ≥ 10/MB as AH-TMBH. A subset of pts treated with ICIs at DFCI and of EUR ancestry were analyzed. TMB was intentionally mis-calibrated in EURs (MC-TMB), to mimic the TMB overestimation observed in non-EURs. Associations between TMBH status and overall survival (OS) was assessed using Cox regression. Results: Uncalibrated TMB was significantly higher in tumors from non-EUR pts overall (p

BACKGROUND Academics in all disciplines increasingly use social media to share their publications on the internet, reaching out to different audiences. In the last few years, specific indicators of social media impact have been developed (eg, Altmetrics), to complement traditional bibliometric indicators (eg, citation count and h-index). In health research, it is unclear whether social media impact also translates into research impact. OBJECTIVE The primary aim of this study was to systematically review the literature on the impact of using social media on the dissemination of health research. The secondary aim was to assess the correlation between Altmetrics and traditional citation-based metrics. METHODS We conducted a systematic review to identify studies that evaluated the use of social media to disseminate research published in health-related journals. We specifically looked at studies that described experimental or correlational studies linking the use of social media with outcomes related to bibliometrics. We searched the Medical Literature Analysis and Retrieval System Online (MEDLINE), Excerpta Medica dataBASE (EMBASE), and Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases using a predefined search strategy (International Prospective Register of Systematic Reviews: CRD42017057709). We conducted independent and duplicate study selection and data extraction. Given the heterogeneity of the included studies, we summarized the findings through a narrative synthesis. RESULTS Of a total of 18,624 retrieved citations, we included 51 studies: 7 (14%) impact studies (answering the primary aim) and 44 (86%) correlational studies (answering the secondary aim). Impact studies reported mixed results with several limitations, including the use of interventions of inappropriately low intensity and short duration. The majority of correlational studies suggested a positive association between traditional bibliometrics and social media metrics (eg, number of mentions) in health research. CONCLUSIONS We have identified suggestive yet inconclusive evidence on the impact of using social media to increase the number of citations in health research. Further studies with better design are needed to assess the causal link between social media impact and bibliometrics.

472 Background: Enfortumab Vedotin (EV), an antibody-drug conjugate that targets nectin-4, is approved for metastatic urothelial carcinoma (mUC) progressing post-platinum and PD1/L1 inhibitor therapy. Erdafitinib is approved in patients for post-platinum mUC with activating genomic alterations in FGFR2/3, but the activity of EV in this subset is unclear. We investigated the activity of EV in patients (pts) with mUC based on FGFR2/3 genotype to inform management. Methods: In this multi-center, retrospective analysis, we assessed the objective response rate (ORR) to EV in mUC pts with and without FGFR2/3 genomic alterations detected by targeted panel next-generation sequencing. Activating gene fusions and known hotspots mutations in the two genes were considered. Descriptive analysis of ORR and patient characteristics was performed. Fisher’s exact test and binomial test with two-tailed p-value were used. Results: 40 pts were available from 4 institutions. Most pts were male (31/40, 78%) and the median age at start of EV was 74.1 (range 49 – 90) years. Ten patients (25%) had upper tract urothelial carcinoma (UTUC), and 33 (82%) had baseline ECOG performance status of 0-1. 31 of 39 patients had received both platinum-based chemotherapy and PD1/L1 inhibitors. Seven patients had confirmed activating hotspot FGFR3 mutations (p.S249C or p.Y373C). One pt had FGFR2 high-level amplification (HA), and one had FGFR3 HA. Of 36 patients evaluable for ORR, 18 had partial response (PR), 12 had stable disease (SD) and 6 had progressive disease (PD). Patients with FGFR2/3 activating mutations exhibited an ORR that was not statistically different compared to patients without no mutations: 2/7 (29%; 90% CI: 5 – 66%) vs. 16/29 (55%; 90% CI: 38 – 71%) respectively ( p-value = 0.4). 3/7 patients with FGFR3 hotspot mutations received an FGFR2/3 inhibitor and none responded; one of them had a sequential response to EV. Conclusions: In this multi-center retrospective cohort, FGFR2/3 activating genomic alterations did not appear to compromise response to EV in mUC. Larger studies are required to confirm our findings and optimal sequencing of EV and erdafitinib in mUC pts with FGFR2/3 genomic alterations requires further assessment.

489 Background: Immune checkpoint inhibition (ICI) has greatly improved clinical outcomes for pts with mUC and other cancers. ICI is associated with a class of AEs, deemed irAEs due to immune activation. Nonetheless, biomarkers associated with irAE are still lacking. We hypothesized that the immune response against neoantigens is partly responsible for irAEs and investigated the association between irAEs, TMB and response to ICI. Methods: We identified patients with mUC at Dana Farber Cancer Institute who were treated with ICI (monotherapy or combination) and had available tumor sequencing data through Oncopanel. TMB was calculated using the number of non-synonymous exonic mutations per megabase. The severity of irAEs was graded using CTCAE v.5.0. Mann-Whitney U test was performed to identify association between TMB, incidence and grade of irAEs. A cut-off of 10/mb was assigned for TMB. Fisher’s exact test was used to evaluate the radiologic response between pts with and without irAEs and low vs. high TMB. Multivariable linear regression was used to assess the relationship between TMB, irAEs and response. p-values were adjusted using Benjamini-Hochberg method. Results: Of 101 pts with mUC who met the inclusion criteria, 32 (32%) reported irAEs. 6 (6%) were grade (G)1, 20 (20%) were G2, and 6 (6%) were G3. Median(m) time on therapy was 84 days for pts without irAEs and 88 days for pts with irAEs. Pts with irAEs had higher mTMB (15.4/mb) compared to pts with no irAEs (9.8) ( p = 0.01). In pts on monotherapy (93), those with irAEs (n=27) had a higher mTMB (15.13/mb) compared to pts with no irAEs (n=66) (mTMB = 10.20/mb) ( p = 0.01). Out of 94 pts with radiological data, response was achieved in 16 (50%) pts with irAE vs 10 (16%) pts with no irAE ( p < 0.001). When both irAE and response were included in a multivariable regression, the association between irAE and TMB was not significant ( p = 0.4). Pts with both irAE and high TMB had a response rate of 56% which was significantly higher than those with either irAE but low TMB (28.6%) or high TMB but no irAE (21.2 %) or low TMB and no irAE (10.3%) (Chi-square test p = 0.002; FDR corrected p-values for individual comparisons in Table). There was no association between TMB and irAE grade. Conclusions: Higher TMB was associated with higher incidence of irAEs in pts with mUC on ICIs. Moreover, pts with both high TMB and irAEs exhibited better response rates than those with only high TMB or irAEs, suggesting that they may provide complementary tumor and host characteristics. Further evaluation in mUC is needed to confirm this relationship between TMB, irAEs and response in a larger cohort and explore specific mutational signatures that may be associated with irAEs. [Table: see text]

475 Background: ICB has shown clinical benefit across several metastatic carcinomas; however, predictive biomarkers are still lacking. CDKN2A is one of the most commonly altered genes across human cancers. With prior studies giving conflicting evidence regarding the association between CDKN2A alterations and ICBs, we examined the impact of CDKN2A alterations on clinical outcomes in UC patients treated with ICBs. Methods: Of 809 patients at the Dana Farber Cancer institute (DFCI) treated with ICBs only and with relevant cancer types and targeted exome sequencing data (Oncopanel), 235 (29%) had loss-of-function (LOF) mutations or homozygous deletions in CDKN2A. Overall survival (OS) was compared by Cox logistic regression between CDKN2A altered and CDKN2A wild type (WT) patients. Hazard ratio (HR) was derived using multivariable analysis (MVA), adjusted for prior lines of therapy and tumor mutational burden (TMB). A validation cohort from Memorial Sloan Kettering Cancer Center (MSKCC) (Samstein et al., Nature Genetics, 2019) of 811 cancer patients treated with ICBs was analyzed in a similar manner, adjusted for TMB. As a control, the association between CDKN2A alterations and OS was examined in a cohort of platinum-treated UC patients (N = 56) to determine whether CDKN2A alterations were predictive of response to ICIs. Results: For the DFCI and MSKCC cohorts, median follow-up was 26.9 and 24 months (m), respectively. In the DFCI and MSKCC cohorts, CDKN2A alterations were found in 32/90 (35%) and 22/104 (21.2%) of UC, respectively; 4/55 (7.3%) and 3/131 (2.3%) of renal cell carcinoma, respectively; 73/178 (41%) and 45/194 (23.2%) of melanoma tumors, respectively; 86/370 (23.2%) and 26/260 (10%) of non-small cell lung cancer (NSCLC) tumors, respectively; 18/66 (27.2%) and 4/53 (7.5%) of esophagogastric tumors, respectively; and 22/50 (44%) and 11/69 (15.9%) of head and neck, respectively. CDKN2A alterations were significantly associated with shorter OS and TTF in the DFCI UC and melanoma cohorts by MVA, and showed a trend towards significance in the MSKCC UC cohort (Table). There was no significant association between CDKN2A alterations and OS for the other cancer types in both cohorts; and no association with OS or TTF was seen in the DFCI cisplatin-treated UC cohort. Conclusions: CDKN2A alteration status may serve as a predictive biomarker in patients with UC treated with ICBs. Further studies are needed to examine the mechanism of this clinical effect. [Table: see text]

467 Background: The genetics of urothelial carcinoma (UC), the most common histology of urinary tract (UT) tumors, is well characterized; much less is known about the genomic features of rare histologic variants of UT tumors. We aim to compare the genomic alterations (GA) of UT tumors with adenocarcinoma (AD), small cell (SC), squamous cell (SQ), or plasmacytoid (PC) histologies, to UC tumors. Methods: We identified patients with pure variant (AD, SC, SQ, PC) or UC histology with genetic characterization through the GENIE registry. Patient tumor genomic data were captured by Memorial Sloan Kettering Cancer Center (MSK)-IMPACT and Dana-Farber Cancer Institute (DFCI)-Oncopanel NGS initiatives. Tumors with mixed histology were excluded. We limited our analysis to genes tested >1000 times (N=211). Mutation frequencies and copy number variants (CNVs), collectively called GAs, were determined for AD, SC, SQ, PC, and UC, and were compared using the Fisher’s Exact test and Kruskall Wallis test. Nominal p values were obtained, and FDR correction was employed (q < 0.1). Results: We identified 1199 patients with available genomic data who met the inclusion criteria. Histologic distribution was: 32 AD, 13 SC, 15 SQ, 11 PC, and 1128 UC tumors. The median age was 68 years and 77% of patients were male. Statistically significant differences in genetic alterations by subtype are shown in the table below. ARID1A and KDM6A GAs were higher in UC; PC and SC; CDH1 GAs higher in PC; RB1 and TP53 GAs higher in SC; SMAD4 GAs higher in AD; and NFE2L2 GAs higher in SQ. Conclusions: Variant UT histologies exhibit a distinct pattern of alterations compared to UC, consistent with their divergent clinical behavior. This suggests different biological origins for these variant histologies and possibly different therapeutic vulnerabilities. Exploring the GAs of these UT tumors in larger datasets is warranted. [Table: see text]

659 Background: Hereditary RCCs account for 3-5% of all RCC cases. The prevalence and significance of germline PVs of RCC have not been fully characterized. Methods: We evaluated the frequency of pathogenic and likely pathogenic variants, referred to as PVs, in 1829 high-risk RCC pts who underwent targeted clinical germline testing (1-134 genes) at a commercial laboratory. PVs, including single nucleotide variants/indels/ copy number variants, were confirmed using orthogonal technology in accordance with Invitae’s standard operating practices. Actionable genes were defined as established cancer-predisposition genes that confer a higher risk for any cancer phenotype and for which enhanced screening and family genetic testing are recommended by the National Comprehensive Cancer Network. We focused our analysis on genes tested in more than 100 pts (n=93). Results: Among 1892 pts, 54.9% were male, and 68.9% were Caucasians, with median age 50 (range:1-87) years at RCC diagnosis. 11.8% (n=215) of pts had at least 2 primary RCCs, and 30.7% (n= 561) had a personal history of another cancer. The cumulative frequency of pts with PVs was 17.7%. PVs in known RCC susceptibility genes such as FH, FLCN, and SDHB were detected in 1.8% (29/1622), 1.22% (120/1634) and 0.64% (11/1727) of pts respectively. PVs in other cancer-associated genes were most frequently reported in CHEK2 (loss-of-function variants, 30/1276, 2.4%), MUTYH (19/1124, 1.7%), and BRCA2 (17/1276, 1.33%). PVs in DNA-damage repair genes (DRG) accounted for 71.8% of PVs and, overall, were detected in 12.7% of pts. Among the DRG, PVs in the homologous recombination pathway (ATM, BARD1, BLM, BRCA1, BRCA2, BRIP1, CHEK2, NBN, PALB2, RECQL4, WRN) were the most prevalent (7.8%) whereas the mismatch repair pathway (MLH1, MSH2, MSH6, PMS2) was altered in only 0.7% of pts. Of the examined cohort, 9.7% of pts had ≥1 actionable PV. In non-Caucasians, BRCA2 PVs were the most common (6/273, 2.20%). Conclusions: PVs were identified in 17.7% of RCC subjects, most of which (71.8%) were in DRG, with »10% of pts having actionable variants. Our work is concordant with known RCC susceptibility genes and potentially highlights novel risk genes that should be validated in future studies.