Their study focused on how the community of bacteria living in a patient’s gut, known as the intestinal microbiota, might determine whether they experience gastrointestinal issues during radiotherapy for prostate cancer.

The intestinal microbiota identifies the complex assemblage of all microbes residing in our intestines. Here, microbial diversity appears to be a key factor associated with several conditions, including inflammatory bowel disease, irritable bowel syndrome, obesity, and colorectal cancer.

The team analysed samples and data of 215 prostate cancer patients from the Micro-Learner observational study. During radiotherapy, the severity and typology of patients’ gastrointestinal side effects were monitored weekly, and an average score was used to identify patients experiencing sustained gastrointestinal problems. In parallel, patients’ stool samples were collected before radiotherapy to sequence the characteristic bacterial gene ‘16S rRNA’, from which the abundance of different bacteria in the patients’ gut could be quantified.

The analyses revealed that reduced bacterial diversity in the gut before radiotherapy was associated with an increased risk of radiation-induced side effects.

Moreover, the team discovered that the abundance of specific types of bacteria was linked to a higher risk of gastrointestinal side effects. These key bacteria included the genera Faecalibacterium, Bacteroides, Parabacteroides, Alistipes, Prevotella, and Phascolarctobacterium. With this information, the team developed a machine learning clinical decision-tree model that assesses the relative abundance of these bacteria in a stool sample, and predicts a patient’s risk of adverse effects during prostate cancer radiotherapy.

This study has important implications for the future of prostate cancer treatment. By analysing a patient’s gut bacteria before starting radiotherapy, clinicians can predict who is at a higher risk for gastrointestinal side effects. The ability to predict which patients might experience significant side effects would allow doctors to tailor their treatment plans to minimise doses to normal tissues. New strategies could also be developed to prevent or lessen these side effects, such as using probiotics to predispose the gut microbiota to radiotherapy before it starts.

The work highlights the potential of the gut microbiota in personalised cancer treatment. As more studies build on these findings, the ambition of truly personalised medicine becomes ever more achievable, promising a future where cancer treatments are not only more effective but also gentler on patients’ quality of life.