Metformin use and the risk of incident breast cancer: a systematic review and meta-analysis accounting for time-related biases, and why imeglimin cannot yet be evaluated

Background: Observational studies have suggested that metformin lowers breast cancer risk, but many were susceptible to immortal time and time-window bias. Imeglimin, a structurally related glucose-lowering drug approved in Japan in 2021, has been proposed as a candidate for cancer prevention. Methods: We searched PubMed (1 November 2026) and the reference lists of earlier meta-analyses for cohort and case-control studies that reported breast cancer-specific estimates for metformin use and incident breast cancer. One report per source population was pooled with a DerSimonian-Laird random-effec

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