Background & AimsImmune checkpoint inhibitors (ICIs) can restore exhausted T cell immunity not only for cancer treatment but also potentially for curing chronic hepatitis B (CHB). The impact of ICIs on Hepatitis B surface antigen (HBsAg) seroclearance in cancer patients was unclear. MethodsConsecutive cancer patients from 2016 to 2020 (Cohort 1, n=118), and hepatocellular carcinoma (HCC) patients from 2020 to 2022 (Cohort 2, n=44, as validation) receiving ICIs and positive for HBsAg were retrospectively recruited. An additional hepatitis B virus (HBV)-HCC cohort (Cohort 3, n=85) without ICI served as a control group. Factors associated with HBsAg loss or combining HBsAg decline >1 log were analyzed. ResultsWith median follow-up of 17.5 months, 8 (6.8%) in cohort 1 and 4 (9.1%) in cohort 2 achieved HBsAg seroclearance, and additional 4 in cohort 1 and 1 in cohort 2 had HBsAg decline >1 log. In multivariate analysis, HBsAg <100 IU/mL was associated with HBsAg seroclearance (HR=6.274, p=0.028). In the validation cohort, the cumulative incidence of HBsAg loss at months 12 and 24 was 13.0% and 38.4% for baseline HBsAg <100 IU/ml, which were significantly higher than those in the control group (p=0.0267). While no case in cohort 3 achieved HBsAg within 24 months. Of the 17 cases achieved HBsAg loss and decline >1 log, 16 (94.1%) had nucleos(t)ide analogs treatment. The median time to HBsAg loss or HBsAg decline was 16.5 months (ranged 9.6 to 27.5). ConclusionsICIs may accelerate HBsAg seroclearance in cancer patients with baseline HBsAg <100 IU/ml. This finding provides important information for the design of future ICI trials to achieve functional cure in patients with CHB.