Introduction: Although the efficacy of testosterone for the treatment of hypoactive sexual desire disorder is well established, the effect of testosterone therapy on breast cancer risk remains uncertain.
Aim: The incidence of invasive breast cancer among past and current testosterone users.
Methods: Retrospective cohort study of 631 women ever treated with testosterone between January 1989 and December 2007 in a clinical endocrinology practice.
Main outcome measure: The incidence of invasive breast cancer since first exposure, and the standardized incidence rate ratio (IRR) calculated using Australian age-specific incidence rates for 2005.
Results: The mean age of the women at first exposure to testosterone therapy was 49.1 +/- 8.2 years, median treatment duration, 1.3 years, and mean follow-up of 6.7 +/- 4.6 years, providing 4,015 woman-years of follow-up. Twelve cases of invasive breast cancer occurred among 599 women breast cancer-free before treatment, giving an age adjusted IRR of 1.35 (95% confidence interval 0.76-2.38). There was no evidence of an independent effect of duration of exposure on breast cancer risk.
Conclusion: In this study, testosterone use was not associated with a significant increase in breast cancer risk.