Uncertainty about estrogen alone
January 31, 2011
January 31, 2011 — Breast cancer risk associated with combination hormone replacement therapy (HRT) is greater if the therapy is started soon after menopause, according to the results of the observational Million Women Study conducted in the United Kingdom.
Among current users of estrogen–progestin formulations, the relative risks for breast cancer were greater if use began less than 5 years after menopause (relative risk [RR], 2.04; 95% confidence interval [CI], 1.95 to 2.14) than if it began 5 years or more after menopause (RR, 1.53; 95% CI, 1.38 to 1.70).
The findings, by Valerie Beral, MD, from the University of Oxford in the United Kingdom, and colleagues were published online January 28 in the Journal of the National Cancer Institute.
These results about the timing of combination HRT provide “substantial support” for the findings of the Women’s Health Initiative (WHI) in the United States and the French E3N cohort, according to an editorial that accompanies the study.
“Many other findings” from the Million Women Study also parallel those of the WHI, according to the editorialists, Rowan T. Chlebowski, MD, PhD, from Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, in California, and Garnet Anderson, PhD, from the Fred Hutchinson Cancer Research Center in Seattle, Washington.
“In both [studies], the use of an estrogen–progestin formulation for a moderate duration was associated with increased breast cancer incidence. An increased risk of breast cancer was also associated with increased hormone use duration, increased risks of node-positive disease, and breast cancer mortality. Both studies also observed that breast cancer incidence rates declined rapidly after cessation of estrogen–progestin formulation use,” they write.
Overall, for women who used combination HRT, compared with control subjects, there was a 39% increase in the relative risk of developing breast cancer in the Million Women Study and a 26% increase in the WHI trial, which the editorialists call “consistent” findings.