Prophylactic antibiotic use is associated with better clinical outcomes in gastric cancer patients receiving immunotherapy.

Background: The relationship between antibiotic treatment and immunotherapy efficacy is complex.

Methods: This study was a single-center study. History of antibiotic use in gastric cancer (GC) patients within 1 or 3 months prior to immunotherapy was collected. Patients were categorized into 3 groups according to whether they had used antibiotics prior to immunotherapy: none, prophylactic use, and infection.

Results: A total of 252 GC patients received immunotherapy, of which 38.5% (97/252) received antibiotic treatment within 1 month before immunotherapy (prophylactic use in 72.2% of patients) and 48.8% (123/252) received antibiotic treatment within 3 months before immunotherapy (prophylactic use in 74.8% of patients). The prophylactic use of antibiotic within 1 month prior to immunotherapy significantly improved overall survival (OS) compared with patients who received anti-infective therapy and had no history of antibiotic use (prophylactic vs infection: OS, 22.6 vs 9.7 m, HR, 0.53, 95% CI, 0.27-1.07; prophylactic vs none: OS, 22.6 vs 14.7 m, HR, 0.57; 95% CI, 0.39-0.83). The use of antibiotics in infected patients did not increase the risk of death in patients compared with those who did not use antibiotics. Prophylactic antibiotic use within 1 month before immunotherapy is an independent prognostic factor for OS.

Conclusions: Prophylactic use of antibiotics is associated with better prognosis in GC patients receiving immunotherapy. Therefore, there is no necessity to delay the use of immune checkpoint inhibitors in this group of patients.