The Relationship between Metformin Consumption and Cancer Risk: An Updated Umbrella Review of Systematic Reviews and Meta-Analyses.
Level 3 - non-randomized controlled study
Umbrella review of systematic reviews and meta-analyses derived predominantly from observational studies (594 observational vs. 26 randomized controlled trials).
PubMed 37854987 · doi:10.4103/ijpvm.ijpvm_62_21
What was done
An umbrella review systematically searched Scopus, PubMed, Embase, Cochrane, Web of Science, Google Scholar, and reference lists from database inception to March 24, 2020. The authors synthesized evidence from 36 meta-analyses encompassing 620 original research studies (26 randomized controlled trials and 594 observational cohort and case-control studies) assessing metformin use and the risk of 15 cancer types.
What was found
Metformin was associated with statistically significant risk reductions in multiple cancers: liver (OR 0.59, 95% CI: 0.47 to 0.74), pancreatic (OR 0.59, 95% CI: 0.50 to 0.69), cervical (OR 0.60, 95% CI: 0.43 to 0.83), head and neck (OR 0.71, 95% CI: 0.61 to 0.83), colorectal (OR 0.73, 95% CI: 0.59 to 0.91), colorectal adenoma (OR 0.75, 95% CI: 0.65 to 0.86), ovarian (OR 0.76, 95% CI: 0.62 to 0.93), colon (OR 0.79, 95% CI: 0.69 to 0.91), esophagus (OR 0.90, 95% CI: 0.83 to 0.98), and lung (OR 0.92, 95% CI: 0.85 to 0.99). Associations were not statistically significant for stomach (OR 0.72, 95% CI: 0.26 to 1.99), breast (OR 0.93, 95% CI: 0.84 to 1.02), prostate (OR 0.94, 95% CI: 0.85 to 1.04), bladder (OR 0.94, 95% CI: 0.64 to 1.38), or endometrial cancer (OR 1.05, 95% CI: 0.82 to 1.35).
Why it matters
This umbrella review maps the broad observational literature on metformin across 15 malignancies, highlighting that inverse associations are strongest for gastrointestinal and gynecological cancers, while negligible for breast, prostate, and bladder cancers.
Limits
The underlying evidence base is overwhelmingly observational (594 of 620 primary studies), making findings vulnerable to residual confounding, protopathic bias, and confounding by indication. The abstract does not report metformin dosage, duration of use, comparator drugs, or the overlap of primary studies across the included meta-analyses.
Cited by
- context Type 2 diabetics taking metformin have a 62% reduced risk of developing pancreatic cancer.