Can Metformin Slow Prostate Cancer on Active Surveillance? New Trial Says No

Active surveillance (AS) is a common approach for men with low-risk prostate cancer, allowing them to avoid or delay surgery or radiation. Because some lab and observational studies suggested that metformin (a widely used diabetes drug) might slow cancer growth, researchers tested whether it could help men on AS stay progression-free longer.

The Metformin Active Surveillance Trial (MAST) was a large, well-designed study involving 408 men with low-risk, localized prostate cancer. Participants were randomly assigned to take either metformin (850 mg twice daily) or a placebo and were followed for up to three years. The main goal was to see whether metformin delayed cancer progression, measured by biopsy results or the need for treatment.

The results were clear: metformin did not reduce the risk of prostate cancer progression. Progression rates were similar in both groups, and there was no meaningful improvement in progression-free survival. While slightly more men in the metformin group had negative biopsies at three years, the difference was not statistically significant.

Importantly, a subgroup analysis found that obese men (BMI ≥30) taking metformin actually had a higher risk of disease progression, a finding that surprised researchers and needs further study.

Bottom line: metformin should not be used to prevent progression in men on active surveillance for low-risk prostate cancer, and caution may be needed in obese patients.

Thompson, D. (2026, January 14). Chronic illnesses increase risk of Botox side effects, experts say. Drugs.com. https://www.drugs.com/news/chronic-illnesses-increase-risk-botox-experts-say-128316.html