A retrospective review of the effect of metformin in metastatic prostate cancer.

Abstract

62 Background: Current treatments of metastatic prostate cancer are mainly hormone therapy and chemotherapy. The anticancer potential of metformin on metastatic prostate cancer remains obscure. In this study, we aim to investigate the significance of patients with prostate cancer taking metformin in addition to their current treatment. Methods: An IRB approved retrospective review of metastatic prostate cancer patients was conducted. Patients were categorized into metastatic castration resistant prostate cancer (mCRPC) or hormone-sensitive prostate cancer (mHSPC). Patients were further stratified to those who received metformin vs. those who did not. Progression free survival (PFS) was evaluated based on PCWG3 and RECIST criteria. 6-month (6MO) PSA response and overall survival (OS) were also evaluated in this study. Results: A total of 281 subjects were included for analysis with a mean age of 70±10. Patients were known to have either mHSPC (n = 205) or mCRPC (n = 75), and taking metformin (n = 66) or not (n = 215). There was no significant difference between metformin groups with respect to PSA response at 6MO (p < 0.73). Among those with a recorded 6MO PSA response, 70.4% (38/54) had a response in the metformin group and 72.9% (140/192) had a response in the non-metformin group. Overall median PFS was estimated to be 17 months, with no significant difference in PFS between metformin groups (16.6 vs 17.3; p < 0.88). Within the mHSPC group, metformin users had a lower risk of progression relative to non-users (HR = 0.89; 95% CI: 0.62 to 1.29). Within the mCRPC group, metformin users had a significantly higher risk of progression relative to non-users (HR = 2.65; 95% CI: 1.4 to 5.0). Median overall survival was estimated to be 81.5 months. There was a significant difference in survival time between metformin groups (148.5 vs 69.4; p < 0.02). Conclusions: No significant differences were found in 6MO PSA response or PFS. There was a significant difference in OS amongst patients who were in the metformin group and those who were not.