Hormone Replacement Therapy Increases Breast Cancer Risk, Study Warns

Women going through menopause should reconsider taking hormone replacement therapy (HRT) for symptoms as a new study published March 29 showed that combined HRT may raise the risk of getting breast cancer.

The Women's Health Initiative (WHI) included several randomized clinical trials and also an observational study that enrolled 93,000 women who were not eligible or were not willing to participate in the trials. Estrogen plus progestin was associated with an increase in both breast cancer incidence and mortality, according to a study in the Journal of the National Cancer Institute. However, most observational studies have linked estrogen plus progestin with more positive outcomes.

To determine the differences between the WHI trial and other observational studies, Rowan T. Chlebowski, M.D., Ph.D., Los Angeles Biomedical Research Institute (LA BioMed) lead researcher and his team examined postmenopausal women, who had no prior hysterectomy with negative mammograms within two years and were either users or non-users of estrogen and progestin combined therapy.

The study determined that the diagnosis for cancers related to hormone replacement therapy is just as dire as for other breast cancers. Therefore, women who use HRT are more likely to die of breast cancer than their non-hormone-taking peers.

"You could fill a basketball arena with the women who get the disease," said Chlebowski. "It seems like you'd want to reach a higher threshold before you take it."

In addition, "because prognosis after a breast cancer diagnosis is similar for combined hormone therapy users and non-users, increased breast cancer mortality on a population basis can be expected," Chlebowski and colleagues stated.

Catherine Schairer, Ph.D., and Louise A. Brinton, Ph.D., both of the National Cancer Institute, question whether the data analyzed from the WHI observational study resolves the differences in tumor prognosis and tumor characteristics when compared to the WHI randomized trial.

"In general, tumors in estrogen plus progestin users in the WHI Observational Study were not significantly different from those in non-hormone users with regard to number of positive lymph nodes or tumor size, but were more likely to be well differentiated and positive for hormone receptors, findings which are similar to other observational studies."