Male breast cancer in users of finasteride and dutasteride: A case-control study

Background: Beside alpha blockers, the 5a-reductase inhibitors finasteride and dutasteride are indicated for the treatment of lower urinary tract symptoms caused by benign prostate hyperplasia. In several case reports finasteride has been associated with male breast cancer. Objectives: To quantify the risk for male breast cancer in users of finasteride and dutasteride. Methods: A case-control study was conducted in the UK CPRD database among men aged 45 years and older. Cases were all men diagnosed with breast cancer during the period 1 January 1992 and 31 December 2011. Controls were matched to cases on age and GP practice in a ratio of 1: 10. Use of finasteride, dutasteride and alpha blockers was assessed prior to the diagnosis of breast cancer as was information on possible confounders (cirrhosis, gynaecomastia). Crude and adjusted odds ratios were estimated using conditional logistic regression analyses. Results: Three hundred and ninety-eight cases were identified and matched to 3,930 controls. Ever use of finasteride or dutasteride was associated with a nonsignificant 25% crude increased risk of breast cancer compared to non-users (OR 1.25, 95% CI: 0.75-2.14). If 1-25 prescriptions had been issued in the 5 years before the index date, no significantly increased risk was observed (OR 1.19, 95% CI: 0.81-1.74). In contrast, men who had received 25-50 prescriptions during the 5 years preceding the index date a significant 84% increased risk compared to non-users (adj. 1.84, 95% CI: 1.07-3.20). Compared to men who used alpha blockers only the relative risk was 0.87 (95% CI 0.48-1.57). Conclusions: Men who were frequently prescribed finasteride or dutasteride over a period of 5 years had an increased risk of breast cancer.