The Gut Microbiome in Surgical Oncology: Mechanisms, Perioperative Outcomes, and Therapeutic Opportunities

INTRODUCTION: The gut microbiome is a fundamental determinant of gastrointestinal physiology. It is essential in maintaining host homeostasis while also implicated in cancer pathogenesis and alteration in physiological response to surgical stress. This narrative review evaluates the microbiome's mechanistic role in surgical oncology, assessing it as a biomarker for risk stratification and an emerging therapeutic target. METHOD: The current literature was synthesized to examine microbial impacts on tumourigenesis and perioperative surgical outcomes across the lower and upper gastrointestinal tracts (including the gut-lung axis), the hepatopancreatobiliary system, and extra-abdominal malignancies (breast cancer and melanoma). RESULTS: Dysbiotic microbial signatures, termed the oncobiome, actively drive tumour progression and immune evasion. Perioperative interventions induce acute microbial shifts linked to serious complications such as anastomotic leaks and pneumonia. Clinically, targeted modulation yields significant benefits as demonstrated by: perioperative synbiotics reducing infectious complications by 45% in colorectal surgery and 64% in major liver surgery. Furthermore, preoperative oral care reduces post-esophagectomy pneumonia by up to 50%, while Helicobacter pylori eradication halves metachronous gastric cancer risk. However, a detrimental "antibiotic paradox" exists in melanoma, where pre-treatment antibiotic exposure severely impairs immune checkpoint inhibitor efficacy. Conversely, faecal microbiota transplantation can reverse this immunotherapy resistance, achieving up to 80% response rates in trials. CONCLUSION: The microbiome is a critical, modifiable determinant of both short-term surgical recovery and long-term oncologic survival. Future surgical oncology practice will need to integrate precision surgical microbiome-mediated biotherapeutics to optimise outcomes in multidisciplinary cancer care.