May 6, 2015
New Analysis Looks at Longer Term Cancer Risks of
Hormone Therapy

Torrance, CA—In the Women’s Health Initiative (WHI) randomized clinical trials, estrogen plus progestin increased breast cancer incidence and deaths from the disease, but estrogen alone in women with prior hysterectomy significantly reduced both incidence and mortality.

Questions remained, however, on the postintervention effects and their duration. A study published recently in JAMA Oncology helps answer them.

“The use of menopausal hormone therapy (HT) continues in clinical practice, but reports are conflicting concerning the longer-term breast cancer effects of relatively short-term use,” according to the authors led by researchers from the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Torrance, CA.

The study team analyzed influence of menopausal hormone therapy on breast cancer incidence in two WHI trials. With a current median follow-up of 13 years, they found a pattern of changing influences over time as to the effect on breast cancer risk.

For the studies, 16,608 women with a uterus were assigned to receive oral conjugated equine estrogens (0.625 mg/d [estrogen]) plus medroxyprogesterone acetate (2.5 mg/d [progestin]) or placebo with a median intervention of 5.6 years, and 10,739 women with prior hysterectomy were assigned to receive the estrogen alone or placebo with a median intervention of 7.2 years.

“In the [estrogen plus progestin] trial, the higher breast cancer risk seen during intervention was followed by a substantial drop in risk in the early post-intervention phase, but a higher breast cancer risk remained during the late post-intervention follow-up,” the authors summarize. “In the estrogen alone trial, the lower breast cancer risk seen during intervention was sustained in the early post-intervention phase but was not evident during the late post-intervention follow-up.”

After reports of increased breast cancer risk with estrogen plus progestin from the WHI randomized clinical trial followed by the Million Women Study observational analysis, use of menopausal hormone therapy decreased dramatically. That affected both combined estrogen-plus-progestin and estrogen-only formulations, even though the risks were different based on formulation.

“The ongoing influences on breast cancer after stopping hormone therapy in the WHI trials require recalibration of breast cancer risk and benefit calculation for both regimens, with greater adverse influence for estrogen and progestin use and somewhat greater benefit for use of estrogen alone,” the article concludes.

U.S. Pharmacist Social Connect