Incidence of breast cancer in a 22-year study of women receiving estrogen-progestin replacement therapy.

Abstract

To review the incidence of breast cancer in a continuous 22-year study of conjugated estrogen-medroxyprogesterone acetate hormone replacement therapy. Eighty-four pairs of continuously hospitalized postmenopausal women who were matched for age, smoking history, and medical diagnosis were treated with estrogen-progestin hormone replacement therapy or placebo in a prospective and double-blind manner for 10 years. In the subsequent 12 years, the women were offered the choice of starting, stopping, or continuing hormone replacement therapy. After the initial 10 years, the incidence of breast cancer in the placebo group was 4.8%, whereas no cancers were found in the hormone replacement therapy group (P = .12). After an additional 12 years of follow-up, the overall incidence of breast cancer in the women who had never taken hormone replacement therapy was 11.5%, whereas no breast cancers had developed in the women who had ever taken hormone replacement therapy (P < .01). These data suggest that the 22-year administration of estrogen-progestin hormone replacement therapy did not increase the incidence of breast cancer in a small group of continuously hospitalized postmenopausal women.