Supplementary Material for: Use of Antibiotics during Immune Checkpoint Inhibitor Treatment Is Associated with Lower Survival in Hepatocellular Carcinoma

<b><i>Background:</i></b> Recent studies suggested that use of antibiotics may interfere with treatment responses to immune checkpoint inhibitors (ICIs). We determined whether concurrent use of antibiotics during ICI therapy was associated with adverse outcomes in patients with advanced hepatocellular carcinoma (HCC). <b><i>Methods:</i></b> This is a territory-wide retrospective cohort study including all advanced HCC patients who received ICIs (nivolumab, pembrolizumab, or ipilimumab) between January 2014 and December 2019. Exclusion criteria included prior liver transplantation and use of cabozantinib, regorafenib, or ramucirumab. The exposure of interest was concurrent antibiotic use within 30 days before or after the commencement of ICI. The adjusted hazard ratio (aHR) of cancer-related mortality and all-cause mortality with antibiotic use was derived by propensity score (PS) matching in 1:2 ratio of covariates including baseline characteristics, causes of cirrhosis, Child-Pugh status, prior HCC treatment, comorbidities, concurrent medications, and laboratory results including alpha fetoprotein. <b><i>Results:</i></b> A total of 395 HCC patients who had received ICIs were included. During a median follow-up of 16.5 months (interquartile range [IQR]: 5.6–44.3), there were 286 (72.4%) deaths including 231 cancer-related deaths. The median time from the first ICI to event was 7.7 months (IQR: 4.0–16.8). PS matching of 56 antibiotic users with 99 nonusers showed that concurrent antibiotic use with ICI was associated with higher cancer-related (aHR: 1.66; 95% CI: 1.08–2.54) and all-cause mortality (aHR: 1.63; 95% CI: 1.17–2.28). <b><i>Conclusions:</i></b> Concurrent antibiotic use during immunotherapy was associated with higher mortality in patients with advanced HCC. Further studies should examine the role of gut dysbiosis on responses to ICI.