Role of the gut microbiome for cancer patients receiving immunotherapy: Dietary and treatment implications.

Immune-checkpoint inhibitors (ICIs) have revolutionised the therapeutic landscape for multiple malignancies and the health of the gut microbiome (GM) is strongly linked with therapeutic responses to ICI. This review explores the implications of diet and medication on the GM for patients receiving ICI. Clinical trials are underway to explore the impact of factors such as faecal microbiota transfer, probiotics, prebiotics, bacteria consortia and a number of dietary interventions on patients receiving ICI. Randomised controlled trials are lacking, and inferences are currently based on short-term clinical and observational studies. Antibiotics should be avoided before ICI initiation, and depending on prospective data, future consideration may be given to temporary delay of initiation of non-urgent ICI if patient has had broad spectrum antibiotics within 1 month of planned treatment initiation. Proton pump inhibitor use should be discontinued when not clearly indicated and potential switch to a histamine H2-receptor antagonist considered. Patients should be advised to minimise animal meat intake and maximise plants, aiming to consume ≥30 plant types weekly. A high fibre intake (>30 g/day) has been seen to be beneficial in increasing the chance of ICI response. Fermented foods may have a beneficial effect on the GM and should be introduced where possible. Ideally, all patients should be referred to a nutritionist or dietician with knowledge of GM before commencing ICI.