Metformin and cancer: active surveillance needed

Key Points:

• The Metformin Active Surveillance Trial (MAST), a Phase III randomized controlled trial in 408 nondiabetic men with low-risk prostate cancer, found no significant benefit of metformin in delaying cancer progression during active surveillance over three years.
• Previous observational studies suggesting metformin’s geroprotective and anticancer effects are likely confounded by biases; rigorous trials, including MAST and others, have largely failed to demonstrate metformin’s efficacy in cancer prevention or treatment.
• Metformin may have some metabolic benefits in prostate cancer patients with advanced disease or those undergoing androgen deprivation therapy, but these effects do not translate into direct anticancer benefits in early-stage or low-risk cases.
• Some smaller trials indicate metformin might reduce recurrence of colorectal adenomas and improve outcomes in endometrial hyperplasia or tamoxifen-associated endometrial changes, suggesting potential niche roles in specific precancerous conditions.
• Overall, metformin is not supported as a general anticancer or anti-aging drug, and its use should be limited to well-defined populations and conditions; moreover, metformin may interfere with exercise benefits, urging caution in broad off-label use.