Clinical trial
Metformin and Cancer Prevention (secondary analyses)
Last updated 2026-07-02· Last reviewed 2026-07-02· 1 min read
Reviewed by the Ultimate Longevity Bible editorial team. Educational reference — not medical advice. See disclaimer.
The observational signal
- Meta-analyses of T2D cohorts: ~20–30% reduction in cancer incidence for metformin-treated vs sulfonylurea-treated patients.
- Consistent for colon, breast, prostate, pancreatic cancers.
Confounding concerns
- Time-varying confounding: metformin users are healthier at baseline than sulfonylurea users.
- Immortal time bias: exposure-window definitions inflate apparent benefit in some analyses.
- Detection bias: metformin users see clinicians more often; cancers detected earlier.
- Corrected analyses reduce but do not eliminate the signal.
RCT evidence
- Randomised metformin-in-cancer trials (as adjuvant, in various cancers): mostly null on overall survival.
- Some prevention-of-progression signals in prostate and breast cancer.
- No robust primary-prevention RCT exists.
TAME relevance
Cancer incidence is one of the composite endpoints in the TAME trial — the first US RCT of an intervention aimed at aging biology rather than a single disease.
- Age Later — Nir Barzilai (2020) — Book.
- Geroscience Hypothesis — Concept.
- Nir Barzilai — Researcher.
- Diabetes Prevention Program (DPP) — Trial.
- Rapamycin vs Metformin (for Longevity) — Comparison.