Metformin use and prostate cancer in Caucasian men: results from a population-based case-control study

Purpose Metformin is a commonly used medication for type II diabetes mellitus. Epidemiologic studies have suggested a decreased relative risk of cancer with metformin use, and preclinical studies of prostate cancer (PCa) have shown antitumor activity with metformin. In this study, we explore the relationship between metformin use and PCa risk in a population-based case-control study. Methods Cases were men aged 35-74 years diagnosed with PCa between 2002 and 2005 in King County, Washington. Controls were frequency matched by age and identified by random digit dialing. Use of metformin was determined from in-person questionnaires regarding medical and prescription history. The relationship of metformin use with PCa risk was evaluated using logistic regression. Results A total of 1,001 cases of PCa and 942 controls were available for analysis. In Caucasian men, metformin use was more common in controls than in cases (4.7 vs. 2.8%, p = 0.04), resulting in a 44% risk reduction for PCa (adjusted OR = 0.56; 95% CI 0.32-1.00). No association was seen in African-American men. Conclusion Metformin use was associated with a borderline significant decrease in the relative risk of PCa in Caucasians. Further study into this relationship is needed to confirm the association and determine the underlying pathways involved.