Survival Outcomes According To The Tumor Mutation Burden And Pd-L1 Expression In Hepatobiliary Tumors

566 Background: Hepatobiliary (HB) tumors are aggressive tumors with emerging evidence for increasing sensitivity to immune checkpoint inhibitors (ICI). Tumor mutation burden (TMB) was found to be a quantitative biomarker associated with production of neoantigens within the tumor and predict the sensitivity to immune therapy. Herein, we explore the TMB, microsatellite instability (MSI) and PD-L1 expression as a potential biomarker of response to immune therapy in HB tumors. Methods: We retrospectively assessed all patients with hepatobiliary malignancies who have undergone next generation sequencing (NGS) between October 2009 and June 2019. We then analysed the tumor mutation burden and PD-L1 of these tumors and also identified frequency of patients with no clinically actionable mutations. Results: In our total 61 patients with HB tumors predominantly were male (62.3%) with mean age of 63 years. Thirty-four patients had hepatocellular carcinoma, 22 patients had cholangiocarcinoma and 5 patients had gallbladder carcinoma. The most common risk factors were smoking status, cirrhosis, alcohol consumption and hepatitis C virus. The mean TMB reported was 3.2 (1.16 – 7.35). MSI was identified in 13 patients and one was indeterminate. Only 17 patients had PD-L1 positive. At least, 37 patients had one clinically actionable mutation while 24 patients had no clinically actionable mutations. Mean overall survival was 16.6 months, but no statistically significant difference was found by high PD-L1 (3 vs 3.7 months, p=0.3) expression. Conclusions: Our data suggests the TMB in HB tumors is low in general irrespective of their underlying risk factors. We also noted more than half had microsatellite stable tumors and PD-L1 expression. Future larger studies are needed to evaluate TMB, MSI and PD-L1 as a potential biomarker in hepatobiliary tumors to help select patients that will benefit from immune therapy.