A Randomized Phase 3 Trial of Metformin in Patients Initiating Androgen Deprivation Therapy as Prevention and Intervention of Metabolic Syndrome: The PRIME Study.

[PURPOSE] We investigated whether metformin decreases metabolic syndrome (MS) risk in patients with prostate cancer (PCa) receiving androgen deprivation therapy (ADT).

[MATERIALS AND METHODS] In this phase 3, multicenter, double-blind, randomized controlled trial, normoglycemic patients with PCa planned for at least 9 months of ADT were randomized 2:1 to receive metformin 850 mg or placebo twice daily orally for 18 months. The primary objective was to compare proportions of MS at 18 months between the study arms.

[RESULTS] Between July 2018 and November 2023, 166 patients were randomized. The trial closed prematurely on November 24, 2023, because of drug supply cessation and the planned enrollment numbers (n = 300) were not met. A total of 90 (metformin) and 45 patients (placebo) were analyzed in the final analysis. The median follow-up was 24 months (IQR: 19.5-36 months). Proportions of MS between metformin and placebo arms were 38/90 (42%) vs 26/45 (58%) at baseline ( = .09) and 40/73 (55%) vs 23/34 (68%) at 18 months ( = .2). Significant reductions in mean (SD) body weight occurred with metformin at 9 (-0.9 [4] vs +1.8 [3.8] kg; < .001) and 12 months (-0.33 [3.9] vs +1.8 [3.9] kg; = .004). Mean (SD) hemoglobin A1c was lowered with metformin at 9% (-0.02% [0.23%] vs +0.08% [0.26%];  = .02) and 12 months (+0.03% [0.27%] vs +0.08% [0.27%];  = .03). Significantly smaller increments in mean (SD) waist circumferences were noted with metformin at 9 (+0.8 [4.3] vs +2.9 [5.7] cm; = .03), 12 (+1.9 [5.1] vs +3.3 [6] cm; = .15), and 18 months (+1.8 [3.8] vs +3.8 [6.1] cm; = .03).

[CONCLUSIONS] Metformin did not reduce the risk of MS in patients with PCa on ADT. However, significant improvements in body weight, waist circumference, and hemoglobin A1c suggest a potential role for metformin in reducing ADT-related complications.