Study Questions Link Between HRT and Breast Cancer

A new study raises some questions about the link between breast cancer and hormone replacement therapy (HRT), such as the popular medication Prempro. 

South African researchers indicate there were major flaws in The Million Women Study, a U.K. project that linked breast cancer to hormone treatments designed to stave off the effects of menopause.

Those flaws may have biased the results of that study, which suggested that HRT was linked to an increased risk of breast cancer, according to the findings of researchers from the University of Cape Town Medical School.

According to a new report published online by the Journal of Family Planning & Reproductive Health Care on January 16, the Million Woman Study included women diagnosed with breast cancer just months after after starting the study and also included women involved in a breast screening program.

The researchers claim that the Million Women Study “did not adequately satisfy the criteria of time order, information bias, detection bias, confounding, statistical stability and strength of association, duration-response, internal consistency, external consistency or biological plausibility.”

They conclude that while HRT may increase the risk of breast cancer, the Million Woman Study fails to establish a link.

The study does not address the 2002 findings of the National Institutes of Health, which found that women receiving HRT were at a higher risk of breast cancer, strokes and heart attacks. That study, conducted in the U.S., led to about 10,000 breast cancer lawsuits against Wyeth, the maker of the HRT drug Prempro.

Prempro contains a combination of the drugs Provera and Premarin, which artificially boost hormone levels in women undergoing menopause due to surgery or in postmenopausal women. Known as hormone replacement therapy, or HRT, the drugs are designed to provide relief from symptoms such as hot flashes, irregular menstruation or weight gain. Wyeth is now a subsidiary of Pfizer, which has been hit with tens of millions of dollars in compensatory and punitive damages by juries that sided with women who say Prempro caused their breast cancer.

Last month, Pfizer announced that it had set aside a total of $840 million to settle nearly half of the 10,000 claims against it. The company hopes to settle the remaining lawsuits with a set-aside of another $260 million in the first nine months of this year.