Randomized Trial Evaluation of the Benefits and Risks of Menopausal Hormone Therapy among Women 50-59 Years of Age

The health benefits and risks of menopausal hormone therapy among women aged 50-59 years are examined in the Women's Health Initiative randomized, placebo-controlled trials using long-term follow-up data and a parsimonious statistical model that leverages data from older participants to increase precision. These trials enrolled 27,347 healthy postmenopausal women aged 50-79 years at 40 US clinical centers during 1993-1998, including 10,739 post-hysterectomy participants in a trial of conjugated equine estrogens and 16,608 participants with a uterus in the trial of these estrogens plus medroxyprogesterone acetate. Over a (median) 18-year follow-up period (1993-2016), risk for a global index (defined as the earliest of coronary heart disease, invasive breast cancer, stroke, pulmonary embolism, colorectal cancer, endometrial cancer, hip fracture, and all-cause mortality) was reduced with conjugated equine estrogens with a hazard ratio of 0.82 (95% confidence interval: 0.71, 0.95), and with nominally significant reductions for coronary heart disease, breast cancer, hip fracture, and all-cause mortality. Corresponding global index hazard ratio estimates of 1.06 (95% confidence interval: 0.95, 1.19) were nonsignificant for combined estrogens plus progestin, but increased breast cancer risk and reduced endometrial cancer risk were observed. These results, among women 50-59 years of age, substantially agree with the worldwide observational literature, with the exception of breast cancer for estrogens alone.