BETHESDA, Maryland—Researchers abruptly halted a prevention trial of estrogen/ progestin in healthy menopausal women after an independent monitoring committee found a 26% increase in invasive breast cancer among women taking the hormone replacement therapy (HRT). The committee also found that the HRT group had a greater risk of coronary heart disease, stroke, and pulmonary embolism than the placebo group.
The National Heart, Lung, and Blood Institute (NHLBI) stopped the trial, which is a component of the Women’s Health Initiative (WHI), after 5.2 years of average follow-up. The study was scheduled to run until 2005. It was designed to determine whether postmenopausal estrogen/progestin therapy, given to women with a uterus, could prevent heart disease and hip fractures and to determine its risks.
The study involved 16,608 women ages 50 to 79 who were randomized to receive placebo or 0.625 mg of conjugated equine estrogens(Drug information on estrogens) plus 2.5 mg of medroxyproges-terone acetate.
"The cardiovascular and cancer risks of estrogen plus progestin outweigh any benefits, and a 26% increase in breast cancer risk is too high a price to pay, even if there were a heart benefit," said NHLBI director Claude Lenfant, MD.
On the positive side, the WHI results show a 37% reduction in colorectal cancer in the treatment group, a 24% decline in hip fractures, and no difference in mortality from all causes.
A separate WHI study of estrogen-only in women who have had a hysterectomy is continuing because the risks and benefits of estrogen alone remain undetermined. According to the data safety and monitoring board, there is no indication of any increased breast cancer risk in the estrogen-only study.
"When the estrogen-only trial is completed, a comparison of the results of these two trials may provide a better idea of the role of estrogen vs estrogen/ progestin, in health and disease," said Marcia Stefanick, PhD, associate professor of medicine, Stanford University, and chair of the WHI Steering Committee.
