Long-term follow-up of Women’s Health Initiative randomized trials of association of menopausal hormone therapy and ovarian and endometrial cancers

The association of menopausal hormone therapy with risks of ovarian and endometrial cancers is not clear. A Women’s Health Initiative randomized trial randomized postmenopausal women with a uterus to conjugated equine estrogen (CEE) plus medroxyprogesterone acetate (MPA) once daily (n=8506) or placebo (n=8103) for 5.6 years, while a second trial randomized postmenopausal women with a previous hysterectomy to CEE-alone (n=5310) or placebo (n=5,429) once daily for 7.2 years. After 20 years of follow-up, CEE-alone versus placebo significantly increased ovarian cancer incidence (HR 2.04; p=0.14). By contrast, CEE plus MPA versus placebo did not increase ovarian cancer incidence (HR 1.14; p=0.44) but did significantly lower endometrial cancer incidence (HR 0.72; p=0.01).