Metformin may decrease the risk of biochemical recurrence (BCR) among men treated for prostate cancer (PCa), according to a recent systematic review and meta-analysis.

Investigators pooled results from 8 retrospective cohort studies and 1 case-control study published before August 2014. They found that the drug was associated with a marginal 18% decreased risk of BCR and an approximately 50% reduction in the BCR risk among men who received external beam radiation therapy (EBRT), the researchers reported online ahead of print in Prostate Cancer and Prostatic Disease. Metformin use was not associated with BCR risk among men who underwent radical prostatectomy.

“These results suggest that the effect of metformin use on clinical outcomes may differ by type of prostate cancer treatment,” according to the researchers. “A plausible explanation for the beneficial effects of metformin along with EBRT may be the radiation-sensitizing properties of metformin.”

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Metformin was not significantly associated with metastases, all-cause mortality, or cancer-specific mortality. Results were mixed for development of castration-resistant PCa.

These findings should be interpreted cautiously pending prospective, randomized trials, according to the researchers.

“Given the potential for selection bias in the included studies, future observational studies need to adjust for time-variant confounding factors such as primary treatment of prostate cancer, metformin dosage, and adherence to metformin in a robust analytical framework such as propensity-score matching, inverse-probability weighing, or instrumental variable analysis,” the authors concluded.


  1. Raval, AD, et al. Prostate Cancer and Prostatic Disease; doi: 10.1038/pcan.2014.52.