The incidence of invasive breast cancer among women prescribed testosterone for low libido.

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.