Breast Cancer Incidence in Postmenopausal Women Using Testosterone

There is now convincing evidence that non-bio-identical hormone replacement therapy increases the risk for breast cancer. Dimitrakakis et al. of the National Institutes of Health, had previously shown that ovarian androgens normally protect mammary epithelial cells from excessive estrogenic stimulation, and therefore hypothesized that the addition of testosterone to non-bio-identical hormone therapy might protect women from breast cancer.

A retrospective, observational study followed 508 postmenopausal women in South Australia receiving testosterone (implant, average 100mg every 5 months) in addition to synthetic hormone therapy with conjugated estrogens or estrone, in some cases with the addition of a synthetic progestin (medroxyprogesterone acetate or norethisterone).

Breast cancer status was ascertained by mammography at the initiation of testosterone treatment and biannually thereafter. The average age at the start of follow-up was 56.4 years, and the mean duration of follow-up was 5.8 years.

There were seven cases of invasive breast cancer in this population of testosterone users, for an incidence of 238 per 100,000 woman-years. The rate for non-bio-identical estrogen/synthetic progestin and testosterone users was 293 per 100,000 woman-years--substantially less than women receiving non-bio-identical estrogen/synthetic progestin in the Women's Health Initiative study (380 per 100,000 woman-years) or in the "Million Women" Study (521 per 100,000 woman-years).

The breast cancer rate in these testosterone users was closest to that reported for hormone therapy “never-users” in the latter study (283 per 100,000 woman-years), and their age-standardized rate was the same as for the general population.

These observations suggest that the addition of testosterone to conventional hormone therapy for postmenopausal women does not increase and may indeed reduce the hormone therapy-associated breast cancer risk-thereby returning the incidence to the normal rates observed in the general, untreated population.

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