Can Gut Microbiome Testing Help Cancer Patients Reduce Their Risk of Recurrence?

One of the biggest challenges that comes with cancer survivorship is having to deal with the fear of recurrence, as echoed through survivor experiences shared on Our Cancer Stories' patient support platform.

"I'm still fearful today. I am so terrified the cancer will come back, but that fear of recurrence is very normal; everyone goes through it," wrote Elizabeth, a stage 3 colorectal cancer survivor, who was declared cancer-free in 2025 following a 3-year battle with the disease.

"The most challenging aspect of being a cancer survivor is living with the fear of it coming back. It is a constant in my mind. The slightest shortness of breath or a cough can put me on tenterhooks," shared Deb, a stage 1 lung cancer survivor.

Most patients and survivors make positive changes to their diet and lifestyle—both during and after treatment—to improve their chances of recovery and reduce the risks of recurrence.

"I cut down on my smoking, reduced my drinking each week from five drinks to one, and started eating healthier most days," detailed Manuel, a stage 2 prostate cancer survivor, talking about the immediate aftermath following his diagnosis. "I put more effort into eating better, making it an everyday affair."

Such experiences with making lifestyle changes are common. "Post-diagnosis, I started to eat healthy every day and exercise 50% more than I used to," shared Alina, a stage 3 stomach cancer survivor from the United States.

However, these changes are not always easy to implement. Cancer treatment often puts survivors' bodies under significant physical stress, and side effects such as nausea, vomiting, fatigue, loss of appetite, and bowel challenges can make it exceptionally hard to stick to a healthy lifestyle. It can often take days or weeks before survivors begin to feel the positive impact of a healthier diet or new exercise regimen, making it harder to stay consistent. 'Healthier choices' may also differ from person to person; it can be challenging to discern which changes may benefit an individual without a tangible way of measuring their impact.

One up-and-coming solution could involve gut microbiome testing. The gut microbiome refers to the microorganisms that live in our gut, including several species of bacteria, fungi, and viruses. It is the most well-studied part of the human microbiome, known to influence an individual's risk of developing several diseases, including diabetes, cardiometabolic diseases, and cancer. Recent advances in the field suggest that the composition of the gut microbiome can help cancer patients and survivors understand their risk of recurrence and take preemptive action to lower it, both during and after cancer treatment.

The role of the gut microbiome in influencing cancer treatment effectiveness and recurrence

The gut microbiome can influence disease outcomes for those diagnosed with cancer at two distinct stages:

1. During treatment, by modulating the effectiveness of treatment options like immunotherapy or chemotherapy
2. Once in remission, by influencing the factors that contribute to recurrence.

The influence of the gut microbiome during cancer treatment

The role of the gut microbiome in modulating the effectiveness of immunotherapy for cancer treatment has been backed by extensive research. In 2025, researchers at the University of Cambridge found that lipopolysaccharide (LPS), a compound produced by several gut microbiome species, could improve the effectiveness of immune checkpoint inhibitors (ICIs) for cancer treatment.

The gut microbiome has also been shown to impact the effectiveness of other forms of cancer treatment. For instance, a review article from Potiguar University in Brazil found that certain bacterial species metabolize the chemotherapy drug 5-fluorouracil, which is used to treat cancers of the stomach, pancreas, colon, and rectum. Due to these bacteria, the amount of the drug reaching the tumor is markedly reduced, compromising treatment effectiveness.

The influence of the gut microbiome once in remission

In 2024, a review article by the South Australian Health and Medical Research Institute (SAHMRI) found an association between the composition of the gut microbiome and the creation of a tumor growth-promoting environment following cancer treatment. The review, led by Ilaria Pagani, PhD, and Hannah Wardil, PhD, analyzed over 100 studies on the human microbiome and its role in cancer.

Once in remission, the gut microbiome influences cancer recurrence through mechanisms similar to those that enable cancer development in the first place. These mechanisms include chronic inflammation, immune system suppression, and supporting the metabolic requirements of cancer cells. In survivors of colorectal cancer, for instance, an overabundance of the bacterium Fusobacterium nucleatum has been associated with suppressing the anti-cancer immune response, resulting in recurrence.

Gut microbiome testing to prevent recurrence and track the impact of interventions

While nascent, the role of gut microbiome testing in predicting cancer recurrence has been promising. In 2026, researchers from NYU Langone Health and Perlmutter Cancer Center found that the presence of key bacteria in the gut predicted recurrence in melanoma survivors with up to 94% accuracy. In another 2023 study, the gut microbiome emerged as a viable tool to predict the early recurrence of hepatitis B virus (HBV)-related hepatocellular carcinoma, a kind of liver cancer. Though the science still has a long way to go before such experimental data can be translated into a robust clinical diagnostic tool, early findings suggest that gut microbiome tests may one day serve as a useful indicator to reduce uncertainty and support pre-emptive measures for cancer survivors.

Microbiome testing tools like GutID already provide convenient, at-home testing solutions for those looking to understand the composition and diversity of their gut microbiome. However, using such technologies to identify microorganisms that are beneficial or harmful to individuals, based on cancer type, stage, and treatment regimen, remains an emerging area of research. In the future, a clearer understanding of a cancer survivor's microbiome may enable healthcare professionals to recognise and act on early markers in gut composition that could contribute to recurrence.

This article is a collaborative piece with Our Cancer Stories, written by Diya Tibrewal, and is intended for educational purposes only.

Sources

1. Gut bacteria predict skin cancer recurrence, but only when matched for 'Microbial fingerprint.' (2026, April 17). NYU Langone News. https://nyulangone.org/news/gut-bacteria-predict-skin-cancer-recurrence-only-when-matched-microbial-fingerprint
2. Gut microbiome could be key to preventing cancer relapse. (2024, May 2). SAHMRI. https://sahmri.org.au/news/research/gut-microbiome-could-be-key-to-preventing-cancer-relapse
3. NYU Langone Health. Gut Bacteria Predict Skin Cancer Recurrence, but Only When Matched for 'Microbial Fingerprint'.