S2591 Retrospective Analysis of Hepatitis B Reactivation in Patients Undergoing Pembrolizumab Treatment by Country

Introduction: Our objective is to analyze the risk of hepatitis B reactivation in patients undergoing pembrolizumab therapy based on country. Methods: Data from the FDA Adverse Events Reporting System (FAERS) public dashboard was collected on hepatitis B reactivation in patients undergoing Pembrolizumab monotherapy. Data was also collected from FAERS to assess the total number of reported hepatitis B reactivations since 2014, when pembrolizumab was introduced. Both data sets were used to determine a relative risk for hepatitis B reactivation based on the reporting country. Results: From 2014 to 2024, 3472 cases of hepatitis B reactivation were reported to the FAERS dashboard. Thirteen cases were reported in patients undergoing pembrolizumab treatment, approximately 0.37% of all cases. Of the 13 total cases, 7 (53.8%) were from the United States (US), 2 (15.4%) were from China (CN), and 1 each (7.7%) from Great Britain (GB), France (FR), Italy (IT), and Bulgaria (BG). Relative risk for hepatitis B reactivation while undergoing Pembrolizumab treatment was statistically significant in the US and BG; (RR: 8.88, 95% CI: 3.00-26.31, P = 0.0002) and (RR: 48.14, 95% CI: 7.37-314.29, P = 0.0223), respectively. Data from other countries was statistically insignificant. Conclusion: Pembrolizumab functions as a potent check point inhibitor for various immune pathways. Immunotherapy as a class poses a risk of immunosuppression, which can result in hepatitis reactivation. Globally there were approximately 316 million people with hepatitis B in 2019. A staple of initiating immunotherapy is pretreatment screening. Despite pretreatment screening and antiviral therapy for hepatitis B, individuals undergoing immunotherapy develop hepatitis reactivation. Based on the results by country, the US and BG showed statistically significant, elevated RR for hepatitis B reactivation. Regardless of indication, individuals in US and BG undergoing pembrolizumab treatment have an 8.88- and 48.14-fold increased risk of hepatitis B reactivation when compared to individuals on other therapeutic treatment, respectively. This unexpected increased risk in the US and BG is likely due to reporting bias and small sample size. Hepatitis B reactivation is a rare adverse event in patients undergoing pembrolizumab therapy. There is a significant risk for reactivation in patients from the US and BG undergoing pembrolizumab treatment. The overall small sample size of reported events is due to effective pretreatment screening and treatment of hepatitis B.