Feasibility of antibiotic-assisted fecal microbiota transplantation with immunotherapy for esophageal and gastric cancer

This phase I - II, single-institution clinical trial enrolls patients with unresectable advanced or recurrent esophageal or gastric cancer. Participants receive a 1-week course of oral antibiotics (amoxicillin, fosfomycin, and metronidazole) prior to transplantation. A single dose of donor-derived intestinal microbiota solution is administered via colonoscopy, followed by initiation of ICI-based therapy on the next day. The primary endpoint is the incidence of dose-limiting toxicity. Secondary endpoints include response rate, disease control rate, progression-free survival, overall survival, and adverse events. Comprehensive translational research is conducted using stool, blood, and tissue samples to characterize immune responses and identify biomarkers associated with A-FMT and ICI efficacy.<b>Trial registration:</b> jRCTs031240170.The study is ongoing, and patients are currently being enrolled. Enrollment started in June 2024. A total of 7 patients have been enrolled as of August 2025. This protocol is version 3.2.