Case Report: Fecal microbiota transplantation resensitizes advanced non-small cell lung cancer to platinum-based chemotherapy.

Platinum-based chemotherapy remains a key treatment for advanced non-small cell lung cancer (NSCLC) in patients without actionable mutations or response to immunotherapy. Emerging evidence highlights the gut-lung axis as an important factor influencing lung cancer biology and treatment outcomes. Fecal microbiota transplantation (FMT) may restore gut microbial balance and improve anticancer therapy response. However, evidence in patients receiving conventional chemotherapy is limited. We report a case of FMT used to treat refractory Clostridioides difficile infection (CDI) in a patient with advanced NSCLC and evaluate its effects on gut microbial reconstitution and clinical response to chemotherapy. A 64-year-old woman with heavily pretreated NSCLC developed recurrent CDI during eighth-line chemotherapy (etoposide and carboplatin). After failure of standard antibiotic therapy, she underwent colonoscopic FMT. Gut microbiota shifts were analyzed using 16S rRNA long-read sequencing (V1-V10), with taxonomic assignment based on the NCBI 16S database. Following FMT, diarrheal symptoms resolved, and the patient completed the subsequent chemotherapy cycle. Follow-up chest computed tomography showed radiologic improvement, with a reduction in the linear extent of consolidation from 91.4 to 76.7 mm. Microbiological analysis revealed a shift toward gut homeostasis, including increased abundance of Bacillota (formerly Firmicutes), enrichment of Bifidobacterium breve, and depletion of Klebsiella pneumoniae. This case suggests that FMT effectively treats refractory CDI in patients with advanced cancer and may support the efficacy of conventional cytotoxic chemotherapy by modulating the immunometabolic milieu through the gut-lung axis.