Metformin and the risk of endometrial cancer: a population-based cohort study
Abstract
OBJECTIVE: While some observational studies have suggested a protective effect of metformin on incident cancer, concerns about potential bias remain. We compared the incidence of endometrial cancer in metformin versus sulfonylurea initiators. Research design and methods We conducted a retrospective cohort analysis using US healthcare claims (MarketScan®), 2000-2011. We identified new users of metformin versus sulfonylureas with no prior cancer diagnoses and followed them until a diagnosis of endometrial cancer, hysterectomy, treatment change, or disenrollment. We estimated hazard ratios (HR) and 95% confidence intervals (CI) using Cox proportional hazards, using an as-treated analytic approach. Stabilized inverse probability of treatment weights were used to adjust for potential confounding at baseline.
RESULTS: Of 541,128 eligible women, 456,838 (84%) initiated metformin and 84,290 (16%) initiated sulfonylurea. The treatment groups differed at baseline in terms of age and recent diagnosis codes for diabetes, polycystic ovarian syndrome, and endometrial hyperplasia. Over a median follow-up of 1.2 (IQR 0.4-2.3) years and a total of 2,030,914 person-years, 729 women developed endometrial cancer. Metformin initiation was associated with a lower risk of endometrial cancer in the unadjusted analysis (HR 0.81, 95% CI 0.67-0.97). However, after balancing baseline covariates across groups, metformin was not associated with a reduced risk of endometrial cancer (HR 1.09, 95% CI…
How strong is the evidence?
Evidence Hub reads this as a cohort study, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence. Reported size: 541,128 participants or records.
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