295 Background: Hepatobiliary 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 as a potential biomarker of response to immune therapy in hepatobiliary tumors. Methods: We retrospectively assessed all patients with hepatobiliary malignancies who have undergone next generation sequencing (NGS) between January 2013 and September 2018. We then analyzed the tumor mutation burden of these tumors and also identified frequency of patients with no clinically actionable mutations. Results: Of the 65 total patients with hepatobiliary tumors, 49 patients (75%) had at least one clinically actionable mutation while 16 patients (25%) had no clinically actionable mutations. Among 65 patients, 44 patients had hepatocellular carcinoma, 15 patients had cholangiocarcinoma and 6 patients had gallbladder carcinoma. The TMB data is available for 15 patients. The mean TMB reported was 2.7 (1.16 – 4.25), which suggests low mutation burden in general in all our HB tumors. Among the patients with available TMB, the underlying risk factor was noted as hepatitis C in 3, NASH in 1, others in 6, unknown in 5 patients. Conclusions: Our data suggests the TMB in hepatobiliary tumors is low in general irrespective of their underlying risk factors. Future larger studies are needed to evaluate TMB as a potential biomarker in hepatobiliary tumors to help select patients that will benefit from immune therapy.