Open AccessFinasteride treatment and male breast cancer: a register‐based cohort study in four Nordic countries
Author(s) -
Meijer Mathias,
Thygesen Lau Caspar,
Green Anders,
Emneus Martha,
Brasso Klaus,
Iversen Peter,
Pukkala Eero,
Bolin Kristian,
Stavem Knut,
Ersbøll Annette K.
Publication year - 2018
Publication title -
cancer medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.403
H-Index - 53
ISSN - 2045-7634
DOI - 10.1002/cam4.1273
Subject(s) - finasteride , medicine , cohort , rate ratio , incidence (geometry) , poisson regression , confounding , cohort study , male breast cancer , confidence interval , breast cancer , demography , gynecology , cancer , population , environmental health , prostate , physics , sociology , optics
A potential link has been suggested between dispensed finasteride and increased risk of male breast cancer ( MBC ). Due to the rare occurrence of MBC , it remains to be established if such a relationship exists. The purpose of this study was to combine nationwide registers in four countries to assess the potential association between dispensed finasteride and MBC . A cohort of all males with dispensed finasteride in Denmark, Finland, Norway, and Sweden (1,365,088 person years) was followed up for up to 15 years for breast cancer, and compared to a cohort of males unexposed to finasteride. Individual‐level register data included country, dates of dispensed finasteride, MBC diagnosis, and death. Incidence rate ratios ( IRR s) were estimated using a generalized linear model with a Poisson distribution. An increased risk of MBC was found among finasteride users ( IRR = 1.44, 95% confidence interval [95% CI ] = 1.11–1.88) compared to nonusers. The IRR increased to 1.60 (95% CI = 1.20–2.13) when users in Norway and Sweden with short follow‐up time were excluded. The highest IRR was seen among men with medium duration of dispensed finasteride, medium accumulated consumption of finasteride, and among men with first dispensed finasteride prescription 1–3 years prior to diagnosis. The analyses suggested possible ascertainment bias and did not support a clear relationship between dispensed finasteride and MBC . In conclusion, a significant association between dispensed finasteride and MBC was identified. However, due to limited data for adjustment of potential confounding and surveillance bias in the present study, further research is needed to confirm these results.