A Retrospective Study of the Effect of Metformin on Patients with Metastatic Prostate Cancer

INTRODUCTION: Previous studies demonstrated that metformin could lead to an inhibition of proliferation of cancer cells through a shift from anabolic to catabolic metabolism. In this study, we seek to investigate the effect of metformin in metastatic prostate cancer. METHODS: Patients followed at Northwell Health Zuckerberg Cancer Center during 2014-2018 were included if they were diagnosed with metastatic hormone-sensitive prostate cancer (mHSPC) or metastatic castration-resistant prostate cancer (mCRPC), with ⩾6 months follow-up with and without metformin treatment. The primary outcomes, 6-month prostate-specific antigen (PSA) response, overall survival (OS), and radiographic progression free survival (rPFS), were evaluated. RESULTS: There were 267 patients included in the final analysis; 196 patients had mHSPC (73.2%) and 71 had mCRPC (26.8%). Within the mHSPC subjects, there was a significant difference in OS between metformin vs nonmetformin groups (148.5 vs 85.6 months; P < .046) in a univariate analysis; patients who took metformin had a significantly longer OS than subjects who did not (median OS: 148.5 vs 86 months; P < .046). There was no significant difference between the 2 groups with respect to either PSA response rate at 6 months or rPFS or OS in patients with mHSPC in both univariate and multivariate analysis. Within the mCRPC subjects, there was no significant difference between metformin and nonmetformin groups with respect to OS (43.3 vs 51.5 months; P < 0.160) or PSA response at 6 months (38.5% vs 57.1%; p < 0.24); however, patients on metformin had a significantly shorter rPFS in both the univariate analysis (7.3 vs 17.4; P < .0002) and in the multivariate analysis (HR = 2.52; 95% CI: 1.24m 5.11; P < .0109). CONCLUSIONS: Among patients with mHSPC, use of metformin was not significantly associated with improved OS in the multivariate analysis.