Source: China Daily

02-26-2009 10:47

Six years after a landmark federal study established that hormone-replacement therapy (HRT) increases the risk of breast cancer in postmenopausal women, researchers are still trying to tease out exactly how the hormones interfere with women's health. The assumption has always been that stopping hormone therapy would lead to a corresponding drop in breast-cancer risk, but now newly published data from the original trial - the multiyear Women's Health Initiative involving tens of thousands of women - suggest that the benefit occurs much more immediately than previously thought.

The finding is a contentious one. The authors of the new paper, which appears in the Feb. 5 issue of the New England Journal of Medicine, found that the rate of breast cancer in postmenopausal women fell just two years after they stopped hormone therapy and continued to decline yearly. In addition, researchers found that women taking supplemental estrogen and progestin had doubled their risk of breast cancer after five years, compared with women not taking HRT.

The question is why. The authors hypothesize that the decline in breast cancer rates was largely due to the sudden stoppage of hormone therapy. But this correlation, first presented at the San Antonio Breast Cancer Conference in December, has been met with skepticism by other researchers in the community. They raised concerns about drawing a cause-and-effect relationship, since the sharpest decline in women's breast cancer rates occurred in the year after the WHI was halted and its data released, between 2002 and 2003 - too soon to see such a dramatic change in a complex disease like breast cancer, which takes many years to develop.

Samuel Shapiro, a visiting professor of epidemiology at University of Capetown, notes that any cancers that might have existed in breast tissue when these women stopped hormone therapy would not have simply disappeared post-treatment. "Once the growth of a tumor has accelerated, it can't be decelerated," he says. "I'm not aware of any evidence to show that happens."