Finasteride treatment and male breast cancer - a register-based cohort study in four Nordic countries

  • Mathias Meijer
  • Lau Caspar Thygesen
  • Anders Green
  • Martha Emneus
  • Klaus Brasso
  • Peter Iversen
  • Eero Pukkala
  • Kristian Bolin
  • Knut Stavem
  • Annette K Ersbøll

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 (IRRs) 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.

Further information

Original languageEnglish
JournalCancer Cell
Issue number1
Pages (from-to)254-260
Number of pages7
Publication categoryResearch

Collaborative partners

  • National Institute of Public Health, University of Southern Denmark, Copenhagen
  • Department of Nursing, Metropolitan University College, Copenhagen, Denmark. Electronic address:
  • Odense Patient Data Explorative Network, Odense University Hospital and University of Southern Denmark, Odense, Denmark.
  • Institute of Applied Economics and Health Research, Copenhagen, Denmark.
  • Copenhagen Prostate Cancer Center and Department of Urology, Rigshospitalet, Copenhagen, Denmark.
  • School of Health Sciences, University of Tampere, Tampere, Finland.
  • Centre for Health Economics at the University of Gothenburg, Gothenburg, Sweden.
  • Department of Oncology, Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.
  • Department of Economics, University of Gothenburg
  • Health Services Research Unit, Akershus University Hospital
  • Department of Pulmonary Medicine, Medical Division, Akershus University Hospital