Estrogen vs Estrogen Plus Progestin Use in Postmenopausal Women
Posted: Friday, February 21, 2020
In follow-up studies to the Women’s Health Initiative (WHI) trials, Rowan T. Chlebowski, MD, PhD, of the Harbor-UCLA Medical Center, Torrance, California, and colleagues identified that the use of conjugated equine estrogens (CEE) alone in postmenopausal women yielded a reduction in breast cancer incidence and death, whereas the use of CEE plus medroxyprogesterone acetate (MPA) increased breast cancer incidence. These findings were presented at the 2019 San Antonio Breast Cancer Symposium (Abstract GS5-00).
“In contrast to decades of observational study findings, in the WHI trial[s], CEE alone significantly reduced breast cancer incidence and significantly reduced deaths from breast cancer, with these favorable effects persisting over a decade after discontinuing use,” Dr. Chlebowski shared in an American Association for Cancer Research press release. According to the investigators, “CEE alone and CEE plus MPA use have opposite effects on breast cancer incidence. CEE plus MPA use significantly increases breast cancer incidence.”
Researchers enrolled postmenopausal women between the ages of 50 and 79, with no history of breast cancer, in one of two randomized clinical trials from 1993 to 1998 and were followed through 2016. A total of 8,506 postmenopausal women with an intact uterus received estrogen plus MPA versus 8,102 women who received a placebo, for a median of 5.6 years; 5,310 postmenopausal women who had a prior hysterectomy received CEE alone and 5,429 received a placebo, for a median of 7.2 years.
A total of 520 incident breast cancers were reported after 16.1 years in women taking estrogen alone. Those who had received estrogen were 23% less likely to have a breast cancer diagnosis and 44% less likely to die of the disease than those who received a placebo. After 18.3 years, researchers identified 1,003 incident breast cancers in women who received estrogen plus MPA. Those who received estrogen plus MPA were 20% more likely to be diagnosed with breast cancer and to be at an increased risk of death from breast cancer than those taking a placebo.
Disclosure: For full disclosures of the study authors, visit abstractsonline.com.
