Abstract 5132: Multi-omics analysis uncovers predictive biomarkers for the efficacy and outcomes of immune checkpoint inhibitor in combination with chemotherapy in advanced unresectable biliary tract cancers

Abstract Background: Biliary tract cancer, typically diagnosed at advanced stages with a poor prognosis, has witnessed a glimmer of hope in the progress of immune checkpoint inhibitors (ICIs). Yet, their limited response rates necessitate the search for effective biomarkers to refine patient selection. Methods: A total of 125 patients with a confirmed histological diagnosis of unresectable advanced or metastatic biliary tract cancers (BTC) who received first-line ICIs in combination with chemotherapy (chemoimmunotherapy) were prospectively enrolled. All baseline samples from 125 patients underwent targeted DNA sequencing, with an additional 62 patients undergoing RNA sequencing, and 85 patients had accessible mIHC data. The associations between molecular characteristics and the response to chemoimmunotherapy, progression-free survival (PFS) and overall survival (OS) were evaluated. Results: The cohort had a median age of 63 years (range from 34 to 82) and 52. 8% (66/125) were male, including 54 with gallbladder cancer, 57 with intrahepatic cholangiocarcinoma, and 14 with extrahepatic cholangiocarcinoma. The median duration of follow-up was 14. 8 months for the entire cohort, with the median PFS and OS of 6. 9 months (95%CI: 6. 2-7. 9) and 11. 8 months (95%CI: 10. 3-14. 8), respectively. The most mutated genes were TP53 (64/125, 51. 2%), KRAS (34/125, 27. 2%), ERBB2 (18/125, 14. 4%), and ARID1A (17/125, 13. 6%). Mutations of TP53 (51. 2%, p = 0. 042), BRCA2 (4. 8%, p = 0. 002), cytokine genes (6. 4%, p = 0. 004), and high tumor mutation burden (p = 0. 072) demonstrated significant correlation with chemoimmunotherapy response. KRAS G12D mutations (PFS: P 0. 001; OS: P = 0. 034) and ARID1A loss-of-function mutations (PFS: P = 0. 009; OS: P = 0. 012) were adverse survival factors, while high CXCL9 or CTLA4 expression was associated with response (CXCL9, P = 0. 014; CTLA4, P = 0. 067), improved PFS (CXCL9, P = 0. 018; CTLA4, P = 0. 008), and longer OS (CXCL9, P = 0. 010; CTLA4, P = 0. 008) under chemoimmunotherapy. Patients were classified into three subtypes using the identified survival biomarkers. Among them, Type I patients, characterized by the absence of KRAS G12D or ARID1A mutations but expressing high levels of CTLA4 or CXCL9, demonstrated the best outcomes under chemoimmunotherapy. Interestingly, further RNA analysis suggested that elevated CXCL9 expression correlated with heightened immune checkpoint expressions, including CTLA4, PD-L1, and PD-1 (all P 0. 001), as well as increased tumor microenvironment immune activity, findings validated in two additional independent patient cohorts both internal and external. Conclusions: Our study revealed predictive biomarkers relevant to the response and efficacy of immune checkpoint inhibitors in combination with chemotherapy in advanced biliary tract cancer. Citation Format: Jieer Ying, Qi Xu, Jiaojiao Ni, Hanlin Chen, Chaoqun Li, Yanru Xie, Qinhong Zheng, Jianying Jin, Junrong Yan, Xiaoying Wu, Qiuxiang Ou, Li Yuan, Wei Zhuo, Haimeng Tang. Multi-omics analysis uncovers predictive biomarkers for the efficacy and outcomes of immune checkpoint inhibitor in combination with chemotherapy in advanced unresectable biliary tract cancers abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5132.