New findings about breast cancer risk reinforce older ones from the Women's Health Initiative.

In the randomized Women's Health Initiative (WHI) study, postmenopausal women treated with estrogen-progestin hormone therapy (HT) had higher incidence of breast cancer than did placebo recipients (JW Gen Med Jul 26 2002). An observational WHI study paralleled the randomized trial. In this report from the observational study, researchers present data on breast cancer incidence among 41,000 women who had negative mammograms within 2 years of study entry and who used either estrogen-progestin HT (16,000) or no HT (25,000).

During 11 years of follow-up, 2200 invasive breast cancers were diagnosed. With adjustments for numerous demographic and clinical variables, the annual incidence of breast cancer was significantly higher in the HT users than in nonusers (0.6% vs. 0.4%; hazard ratio, 1.55). Breast cancer risk was highest when HT was initiated at menopause (HR, 1.68). In women who commenced HT use within 5 years after menopause, breast cancer risk was significantly elevated, even with <5 years of use (HR, 1.45). Risk for breast cancer followed by death from any cause was higher in HT users than in nonusers (HR, 1.65). Findings were similar in women who adhered to regular mammographic screening.

Comment: These results mirror those of the randomized Women's Health Initiative study. Notably, use of estrogen-progestin hormone therapy close to the time of menopause was associated with highest breast cancer risk. Some clinicians have been advising patients that short-term use is safe in the early postmenopausal period; these findings are at odds with that message. Women should understand that even short-term use just after menopause appears to raise breast cancer risk, although absolute risks are quite small ({approx}2 cases per 1000 patients annually). Lastly, these findings do not apply to women who use estrogen-only HT.

— Allan S. Brett, MD

Published in Journal Watch General Medicine May 21, 2013

CITATION(S):

Chlebowski RT et al. Estrogen plus progestin and breast cancer incidence and mortality in the Women's Health Initiative observational study. J Natl Cancer Inst 2013 Apr 17; 105:526.