502 Background: ICIs are effective agents in metastatic urothelial carcinoma in both platinum-refractory and frontline settings. Responses in patients (pts) with non-urothelial histological variants are not well defined. Methods: We undertook a retrospective analysis of pts with metastatic bladder cancer treated with ICI monotherapy. Pts were identified as having a variant histology if any non-urothelial component was present. Fisher’s exact test was used to assess differences in ORR by histology. Results: Between 12/2014 and 10/2019, 102 pts received ICI monotherapy, of whom 93 were evaluable for response and 33 had variant histology. Median age was 70 yrs, 66% were male, 50% received prior platinum-based chemotherapy. Most received pembrolizumab (66%) or atezolizumab (33%). ORR in the overall cohort was 26% (15% PR, 11% CR), with 12% having SD. Histology breakdown and responses are shown in Table. Although twice as many responses were seen in urothelial pts as in pts with variant histologies (ORR 31% vs 15%), this difference was non-significant (p = 0.14). Conclusions: In this large single-institution cohort, ORR in a heterogeneous population of bladder cancer pts was consistent with data previously reported in clinical trials. Pts with variant histologies had numerically lower responses relative to pure urothelial histology, but this difference was not statistically significant. Clinical benefit to ICIs was seen across multiple variant histologies suggesting potential efficacy in this patient population that should be confirmed prospectively.[Table: see text]

181 Background: KRAS mutations have been widely characterized as markers of poor prognosis in CRC. In stage IV CRC, KRAS mutations are predictive of benefit to anti-EGFR therapy. ctDNA has increasingly been recognized as a prognostic biomarker in CRC as well. We evaluated the association between plasma metabolites and KRAS mutation or ctDNA status in a longitudinal, observational cohort of patients with stage I-IV CRC. Methods: This was a retrospective analysis of prospectively collected blood samples from a single-institute cohort of patients with stage I-IV CRC. All blood samples were collected at pre-chemotherapy baseline. A modified Epi proColon 2.0 CE (Epigenomics AG) assay was used for plasma ctDNA testing on the methylated SEPTIN9 gene (mSEPT9). ctDNA positivity was defined as a mSEPT9 percentage of methylation reference (PMR) value greater than zero. Up to 150 metabolites of central carbon metabolism were analyzed by mass spectrometry and high-performance liquid chromatography. Analytes were compared by relative area under the curve (AUC) and differences evaluated by ANOVA. The mean AUC was used in patients with metabolites measured from > 1 timepoint of collection. Patients were stratified by ctDNA status (positive or negative) and KRAS mutant (MT) or wildtype (WT) status. Results: A total of 32 patients were included with median age 65 years (range 20-90). The majority were female (53%) and had stage IV disease (78%). Of 25 patients with stage IV CRC, 88% had pre-chemotherapy blood samples collected in the first-line setting. Most patients were KRAS MT (44%) compared to KRAS WT (37%) or unknown KRAS status (19%). The most common KRAS MT subtypes were G12D (29%), G12V (29%), G13D (21%), and G12C (14%). The mean overall survival in this cohort was 27.4 months while the mean mSEPT9 PMR value was 2553.6. When stratified by ctDNA status, ctDNA positivity was associated with decreased levels of essential amino acids (lysine, methionine, threonine) and the non-essential amino acid arginine (all p < 0.05). Compared to KRAS WT tumors, KRAS MT tumors were associated with increased levels of proline, phenylalanine, and intermediates of glycolysis (lactate), MTA cycle (SAM, 5-Methioadenosine), and O-GlcNAcylation (GlcNac, all p < 0.05). Conclusions: We are the first to demonstrate the feasibility of associating central carbon metabolites with ctDNA and KRAS mutation status. As ctDNA positivity and KRAS MT status have evolving prognostic potential in CRC, associated metabolic signatures may identify metabolic pathways for novel biomarker development. Our findings also show that KRAS MT CRC appears to be enriched in intermediates of glycolytic, methyl donor, and O-GlcNAcylation pathways.

e15575 Background: Metabolomics is an evolving technique that can offer a non-invasive method for comprehensive identification of metabolic biomarkers. We evaluated the feasibility of measuring plasma metabolites in a longitudinal, observational cohort of patients (pts) with stage I-IV CRC for association with disease characteristics and overall survival (OS). Methods: In this retrospective analysis of prospectively collected blood samples from a single-institute cohort of pts with stage I-IV CRC, up to 150 metabolites of central carbon metabolism were analyzed by mass spectrometry and high-performance liquid chromatography. All blood samples were collected at pre-chemotherapy baseline. Analytes were compared by relative area under the curve (AUC) and differences evaluated by ANOVA. Blood samples were collected from two non-CRC pts to serve as healthy controls. Comparison of plasma metabolite levels were stratified by diagnosis of CRC vs. healthy control, non-metastatic CRC (stage I-III) vs. metastatic CRC (stage IV), and short OS vs. long OS (defined by the median threshold OS of 24.8 months in the cohort). Results: Plasma metabolomics was performed on a total of 32 pts with CRC. The median age of the cohort was 65 years (range 20-90) with the majority being female (53%) and having stage IV disease (78%). Of 25 pts with stage IV CRC, 88% had pre-chemotherapy blood samples collected in the first-line setting and 44% were KRAS mutant compared to 37% KRAS WT and 19% unknown KRAS status. Compared to healthy controls, CRC pts had higher levels of glutamate, nucleotides UMP and CMP, and nucleosides hypoxanthine and inosine (all p < 0.05). When stratified by stage, stage I-III CRC pts had higher levels of the non-essential amino acid (AA) serine and essential AAs threonine and methionine, while stage IV had higher levels of the aldopentose ribose (all p < 0.05) Those with short OS had increased levels in intermediates of glycolysis (lactate, UDP-Glc), glutamine metabolism (GlcNAc), MTA cycle (SAM, 5-Methioadenosine), and pentose phosphate pathway (R5P) as well as increased levels of proline (non-essential AA), phenylalanine (essential AA), thymine (nucleobase), and UDP (nucleotide) compared to pts with long OS (all p < 0.05). Notably, both stage IV and short OS pts had trends in increased intermediates of glutamine metabolism (glutamate, a-KG, UDP-GlcNAc) that did not reach significance. Conclusions: We show that pts with CRC compared to healthy controls and those with stage IV and short OS appear to be enriched in intermediates of multiple bioenergetic pathways including AA synthesis, nucleotide synthesis, glycolysis, methyl donor biology, and glutamine signaling. These findings are hypothesis-generating and can inform more focused evaluation of potential biomarkers and therapeutic targets in CRC.

476 Background: Reliable predictive markers are lacking in patients (pts) with locally advanced or metastatic urothelial carcinoma (aUC) treated with immune checkpoint inhibitors (ICI). We sought to determine whether specific genomic alterations could be used to predict overall survival (OS) in this patient population. Methods: We undertook a retrospective cohort study of pts with aUC who received ICI and underwent genomic profiling by next-generation sequencing (NGS). All patients underwent NGS using commercially available platforms (e.g. Foundation Medicine, Strata, Invitae), or testing on the CLIA-certified institutional panel UCSF500. Associations between the 20 most frequently altered genes and OS were first examined by Cox regression. Genes with a p <0.1 on univariate analysis and relevant clinical variables were then included in a multivariable analysis. Results: We identified 78 pts treated with ICI for aUC with available genomic profiling results. Median age at ICI initiation was 71; the majority of patients had visceral metastases (70.5%), ECOG performance status ≤1 (62.8%) and received ICI in the post-platinum setting (52.6%). Objective response rate in this cohort was 35.9%, median progression free survival was 4.0 months (95% CI 2.6-10.5) and median OS was 17.5 months (95% CI 14.1-NR) from ICI start. The most commonly altered genes were the TERT promoter (TERTp) (61%), TP53 (52%), RB1 (31%), CDKN2A(29%) and CDKN2B (27%). On univariable analysis there was a trend towards longer OS in pts with TERTp mutations (HR 0.53, 95% CI 0.27-1.06, p = 0.07), and shorter OS in pts with CDKN2B mutations (HR 1.91, 95% CI 0.98-3.73, p = 0.06). Both mutations were included in a multivariable analysis. After adjusting for known prognostic variables (ECOG PS, visceral metastases, albumin, hemoglobin, body mass index [BMI], neutrophil to lymphocyte ratio [NLR], and histology), the presence of a TERTp mutation was significantly associated with improved OS (HR 0.30, 95% CI 0.10-0.93, p = 0.04; Table). Conclusions: The presence of a TERTp mutation was an independent predictor of improved OS in a cohort of aUC pts treated with ICI. Other common mutations and clinical variables were not associated with OS on a multivariable analysis. These findings are hypothesis-generating and prospective validation is needed. [Table: see text]

2666 Background: As immune checkpoint inhibitors (CPI) are increasingly approved for the treatment of multiple cancer types, hospitalizations related to severe immune-related adverse events (irAE) will increase in tandem. Here, we identify patients hospitalized due to irAEs and describe survival outcomes across irAE, CPI, and cancer type. Methods: We identified patients exposed to CPIs who were hospitalized from 1/2012 to 12/2020 at our tertiary care hospital by computationally extracting data from the electronic health record. We then performed manual chart review to include only confirmed irAE-related hospitalizations. Survival outcomes were analyzed using Kaplan-Meyer survival curves with log-rank tests. Results: Of 3137 patients treated with CPIs, 117 were hospitalized for irAEs (cumulative incidence 4%). Of these, 36% had melanoma, 15% had lung cancer, 9% had renal cell carcinoma (RCC), and the rest were distributed across other cancers. The average number of irAE-related hospitalizations per patient was 1.25 (ranging from 1-3). Among 153 irAEs requiring hospitalization, 39% were gastrointestinal (GI) (including hepatitis), 12% endocrine, 12% pulmonary, 12% neurologic, 12% musculoskeletal, 7% cardiovascular, 6% dermatologic, and the rest affected other organs. Across all patients hospitalized for irAEs, median survival following hospitalization was 980 days. Patients with GI and endocrine irAEs had longer median survival (1474 days and median not reached [NR], respectively), while patients with pulmonary irAEs had shorter median survival (64 days) [p=0.002]. Patients with melanoma and RCC had longer median survival (2796 days and NR, respectively), while patients with lung cancer had shorter median survival (165 days) [p=<0.001]. Survival was not significantly different across CPI type [p=0.20]. Conclusions: Although hospitalization for severe irAE was rare, these findings suggest that among these patients, survival differs by irAE and cancer type. This real world data can contribute to clinical models that predict the risk of hospitalization and the risk of death due to severe irAEs, which may inform patient counseling and treatment decision-making. [Table: see text]