Estrogen and testosterone not significantly associated with risk for invasive breast cancer

The use of methyltestosterone plus estrogen was modestly, though not significantly, associated with the risk for invasive breast cancer among postmenopausal women from the WHI Observational Study.

The study included 31,842 postmenopausal women followed for a mean of 4.6 years. Researchers took data from the year three visit of the WHI, which was the first to ask about use of exogenous testosterone. They compared estrogen and testosterone users with non-users. Predictors of breast cancer such as prior hormone use and screening mammography were adjusted for when calculating proportional hazard estimates.

At the three-year visit, 35 invasive breast cancer cases were reported among users of estrogen/testosterone. Compared with non-users, women who used estrogen/testosterone had a slightly higher, though nonsignificant, adjusted HR of 1.42.

Women who used estrogen/testosterone for less than one to 12 months had higher rates of invasive breast cancer (HR=1.90; 95% CI, 1.16-3.12) compared with women who used hormone therapy for 13 to 24 months (HR=1.09; 95% CI, 0.61-1.93). The most commonly used preparation of estrogen/testosterone, Estratest (Solvay Pharmaceuticals) resulted in an elevated risk for invasive breast cancer in users compared with non-users (HR=1.78; 95% CI, 1.05-3.01).

Finally, based on previously published data demonstrating the relationship between estrogen/testosterone use and the risk for breast cancer, the researchers examined rates of invasive breast cancer occurrence among estrogen/testosterone users who experienced natural menopause. Though modest, the researchers reported an elevated risk similar to the effect size reported in their study overall (HR=1.57; 95% CI, 0.95-2.61).

Arch Intern Med. 2009;169:41-46.