Metformin as an Adjunct to Progestin Therapy in Endometrial Hyperplasia and Early-Stage Endometrial Cancer: A Systematic Review and Meta-analysis of Randomized Controlled Trials.

Background and objective: Metformin has been studied for its anti-proliferative effects on endometrial cells, and it is hypothesized to have a synergistic effect with progestin therapy in suppressing endometrial cell proliferation. This systematic review and meta-analysis aimed to determine the efficacy of adjunctive metformin in the clinical regression of endometrial hyperplasia and early-stage endometrial carcinoma. There have been previous systematic reviews that investigated the role of metformin with progesterone for endometrial hyperplasia and endometrial cancer, but they have included retrospective cohorts, and are thus have higher risk of bias.

Methods: This meta-analysis followed the Cochrane methodology and adhered to the PRISMA 2020 guidelines. Randomized controlled trials (RCTs) were included if they enrolled reproductive-aged women with endometrial hyperplasia (with and without atypia) and endometrial carcinoma who were treated with progestin and metformin. The primary outcome was the complete response rate at 12-16 weeks, and secondary outcomes included relapse rate, clinical pregnancy rate, and live birth rate. Subgroup analysis of endometrial hyperplasia without atypia vs hyperplasia with atypia and early endometrial cancer was also included. Odds ratios (ORs) and 95% confidence intervals (CIs) were used for dichotomous data.

Results: Six RCTs were included. The addition of metformin to progestin therapy may increase the complete response rate of endometrial hyperplasia without atypia (OR 5.12, 95% CI 1.17 to 22.41; n = 102) and live birth rates (OR 2.51, 95% CI 1.34 to 4.69; n = 188) compared to progestin therapy alone, but the certainty of the evidence is low. Metformin did not have a significant effect on the clinical response of endometrial hyperplasia with atypia and endometrial carcinoma, relapse rates, and clinical pregnancy rates.

Conclusion: Current evidence is uncertain on the potential benefit of metformin with progestin in endometrial hyperplasia and carcinoma. Future high-quality randomized controlled trials with larger sample sizes and longer follow-up periods are needed to support practice recommendations.