Ganguly, Rituparna

4107 Background: Aberrant Wnt/β-catenin activation has been implicated in tumor formation and progression in BTC. CTNNB1 is a key transcriptional co-activator in Wnt signaling. The impact of CTNNB1 alterations on outcomes in intrahepatic (IHCC) vs extrahepatic (EHCC) vs gallbladder (GB) tumors and patterns of gene co-expression is unclear. We examined the molecular correlates and predictive and prognostic significance of CTNNB1 expression in a real-world cohort of pts with BTC. Methods: 7450 BTC tumors were analyzed using Next Generation Sequencing (NextSeq), Whole Exome and Whole Transcriptome Sequencing (NovaSeq) at Caris Life Sciences (Phoenix, AZ). Top quartile transcripts per million (TPM) expression was considered high expressors (Q4), bottom quartile was considered low expressors (Q1) within each subtype. Real-world overall survival (OS) data was obtained from insurance claims. Hazard ratio (HR) was calculated using Cox proportional hazards model, P values were calculated using log-rank test. Significance was determined to be p <0.05. Chi-square and Mann-Whitney tests determined molecular differences between subgroups and adjusted for multiple comparisons (q<0.05). Results: The cohort was comprised of 61% IHCC, 14% EHCC, 23% GB, 2% NOS. CTNNB1 mutations are rare in BTC (1.3%). Pts with CTNNB1-wt tumors had significantly better OS vs CTNNB1-mt (13.6 vs 10.2 mo, HR 0.74, p=0.008). This association remained significant in IHCC (13.2 vs 4.5 mo, HR 0.64, p=0.031) but not EHCC (18.0 vs 11.8 mo, HR 0.87, p=0.64) or GB (12.9 vs 11.0 mo, HR 0.75, p=0.071). CTNNB1-mt tumors were more frequently TP53-mt (63% vs 41%), ERBB2-mt (9% vs 2%) and ATM-mt (9% vs 3%). CTNNB1-wt tumors were more likely BAP-mt (9% vs 0%) and IDH1-mt (10% vs 0%) (all q<0.05). CTNNB1-mt tumors had higher median CTNNB1 expression vs wt (154.9 vs 113.4, q<0.009). Pts with CTNNB1 Q1 expression had significantly better OS vs Q4 (14.5 vs 12.4 mo, HR 0.88, p=0.007). This association held in IHCC (15.0 vs 10.6 mo, HR 0.77, p<0.00001) but not EHCC (17.5 vs 19.9 mo, HR 1.05, p=0.70) or GB (12.4 vs 12.8 mo, HR 1.05, p=0.63). CTNNB1 Q4 expressing tumors were more likely to be TP53-mt (55% vs 34%), PIK3CA-mt (9% vs 5%), KRAS-mt (23% vs 12%) and less likely IDH1-mt (4% vs 14%) compared to Q1 (all q<0.05). CTNNB1 Q4 pts had higher ARID1A, CTLA4, LAG3, HIF1A, TGFB1/2/3, EPHB4, EPHA2, VEGFA expression (FC: 2.1-4.2, all q<0.05) and higher T-cell inflamed score vs Q1. There was a trend towards improved OS in pts with IHCC CTNNB1 Q1 tumors receiving gemcitabine or fluorouracil (17.5 vs 15.0 mo, HR 0.86, p=0.064); no difference in outcomes by CTNNB1 expression in pts receiving immunotherapy. Conclusions: CTNNB1 mutations and mRNA expression levels impact survival in BTC, especially IHCC, and may be associated with benefit from chemotherapy. CTNBB1 alterations are associated with immunogenic, DNA repair and angiogenic pathways and may help identify novel therapeutic strategies for BTC.

4106 Background: The WNT/beta catenin (CTNNB1) pathway plays an integral role in the development of HCC. CTNNB1 has been implicated in HCC progression, metastasis, and drug resistance. We examined associations between CTNNB1 mutations and mRNA expression and clinical outcomes in a real-world cohort of patients with HCC. Methods: 1652 HCC tumors were tested at Caris Life Sciences (Phoenix, AZ) and analyzed with Whole Transcriptome Sequencing (WTS; Illumina Novaseq), Whole Exome Sequencing (NovaSeq,WES) and NextGen DNA sequencing (NextSeq, 592 genes). mRNA expression (transcripts per million) was further stratified into top (Q4) and bottom quartiles (Q1). Kaplan Meier estimates were calculated for overall survival (OS) in the molecularly defined cohorts and estimated from time of tissue collection to last contact. Significance was determined to be p <0.05. Chi-square and Mann-Whitney tests determined molecular differences between subgroups and adjusted for multiple comparisons (q<0.05). Results: Pathogenic CTNNB1 mutations were present in 32% of HCC and mutation status was not associated with CTNNB1 expression level. Pts whose tumors had lower CTNNB1 expression had significantly improved OS, 17.9 vs 12.4 months, Q1 vs Q4, HR 0.72, CI: 0.58-0.89 p=0.002. This association remained significant in patients who received first-line IO (Q1 vs Q4: OS 16.7 vs 10.6 mo, HR 0.54, CI: 0.32-0.94, p=0.025) or TKI (Q1 vs Q4: OS 27.1 vs 17.6 mo, HR 0.60, CI: 0.38-0.94, p=0.025). Low CTNNB1-expressing tumors (Q1) had more frequent ARID1A mutations (15% vs 8%); less frequent TP53 mutations (31% vs 42%); lower VEGFA, EPHB4, EPHA2, HIF1A, TGFB1/2/3 expression, lower MAPK activation and lower T-cell inflamed scores vs Q4 tumors (all q < 0.05). All tumors were MSS. CTNNB1 mutation status (MT vs WT) did not impact survival (OS 17.6 vs 15.3 mo, CTNNB1-MT vs CTNNB1-WT, HR 1.05, CI: 0.91-1.20, p=0.55). Similarly, CTNNB1 mutation status (MT vs WT) did not impact OS in pts treated with IO (19.8 vs 19.6 mo, HR 0.99, p=0.94) or TKI (23.0 vs 22.0 mo, HR 0.86, p=0.33). Conclusions: CTNNB1 mRNA expression, but not CTNNB1 mutation status, is associated with survival in HCC. Patients whose tumors had lower CTNNB1 expression appeared to derive more benefit from immune checkpoint inhibitors and TKI therapy in first line. CTNNB1 expression is associated with DNA repair, immune, neuronal and angiogenic pathways which may pave the way for potential therapeutic opportunities. Further studies are needed to prospectively evaluate CTNNB1 as a biomarker for treatment selection in HCC.