Postmenopausal hormone therapy increases incidence of more advanced breast cancer

Among postmenopausal women, use of estrogen plus progestin hormone therapy (HT) is associated with an increased incidence of more advanced breast cancers and a higher risk for death from breast cancer, according to a randomized, placebo-controlled trial involving more than 16,000 women participating in the Women's Health Initiative.

Researchers gave women aged 50 to 79 years with no history of hysterectomy from 40 clinical centers throughout the United States either 0.625 mg/d combined conjugated equine estrogens plus 2.5 mg/d medroxyprogesterone acetate or placebo and followed them for approximately 11 years.

The researchers found that compared with women in the control group, the women taking the combination hormone therapy had about 25% more invasive breast cancers (385 cases [0.42% per year] vs 293 cases [0.34% per year], respectively; HR, 1.25; 95% CI, 1.07-1.46; P=.004) and that their cancers were almost twice as likely to be node positive (81 [23.7%] vs 43 [16.2%], respectively; HR, 1.78; 95% CI, 1.23-2.58; P=.03).

Chlebowski RT, Anderson GL, Gass M, et al. Estrogen plus progestin and breast cancer incidence and mortality in postmenopausal women. JAMA. 2010;304(15):1684-1692.