Changes in gut microbiota before and after radiotherapy in patients with small cell lung cancer

The association between lung cancer and gut microbiota has drawn increasing attention. Through the gut-lung axis, intestinal microbiota regulates inflammation, metabolites and immune activity to maintain lung homeostasis. This study compared gut microbiota between small cell lung cancer (SCLC) patients and healthy individuals, and assessed microbial changes in SCLC patients before and after radiotherapy. It aimed to identify differential bacterial taxa and metabolic pathways, providing a basis for improving treatment efficacy, guiding immunotherapy, and supporting microbiota-related interventions such as fecal microbiota transplantation. Pathologically confirmed SCLC patients were recruited from the Radiotherapy Department of Ningbo Medical Center Li Huili Hospital. Fecal samples were collected from 13 patients before radiotherapy and 12 after treatment, alongside 15 healthy controls. 16S gene sequencing was used to analyze gut microbiota composition and predict functional pathways. Beta diversity differed notably between SCLC patients and healthy controls. At the phylum level, SCLC patients had higher Proteobacteria abundance. At the genus level, Escherichia-Shigella, Acidaminococcus, Enterococcus, Streptococcus, Megasphaera and Parabacteroides were significantly enriched, while Roseburia, Agathobacter, Lachnospira and Parasutterella were reduced ( P < 0.05). Metabolic pathways and enzyme expression also differed significantly ( P < 0.05). No obvious differences in alpha and beta diversity were found pre- and post-radiotherapy; however, Pasteurellales, Pasteurellaceae and Haemophilus decreased markedly after treatment, with altered predicted metabolic functions ( P < 0.05). SCLC patients showed distinct gut microbiota profiles from healthy individuals, with reduced beneficial bacteria and increased potential pathogenic taxa. Radiotherapy also induced intestinal flora variations in SCLC patients.