Finasteride Treatment and Male Breast Cancer: A Register-Based Cohort Study in Four Nordic Countries

The study analyzed the link between finasteride use and male breast cancer (MBC) in a cohort from Denmark, Finland, Norway, and Sweden, with 1,365,088 person-years of follow-up. It found a 44% increased risk of MBC among finasteride users, with an incidence rate ratio (IRR) of 1.44. The risk was even higher, with an IRR of 1.60, when excluding users from Norway and Sweden with short follow-up times. The greatest risk was seen in men with medium duration of use and those who started finasteride 1-3 years before diagnosis. The study noted potential biases and recommended further research due to limitations such as possible ascertainment bias and the inability to adjust for all confounding factors. Despite these limitations, the study suggested an increased risk of MBC with finasteride use, especially in Denmark and Finland.