HT--breast cancer linkage reaffirmed.(NEWS)

SAN ANTONIO -- Two new statistical analyses of Women's Health Initiative data persuasively indicate that the recent abrupt decline in breast cancer incidence in the United States is attributable to a dramatic drop in the use of estrogen-plus-progestin menopausal hormone therapy and not, as skeptics have argued, to less utilization of mammography.

Academic fencing over causality aside, the practical take-home message from the latest Women's Health Initiative (WHI) data analyses is that the breast cancer risk imparted by hormone therapy (HT) rises sooner and more steeply than previously recognized, and it swiftly declines after HT is discontinued, Dr. Rowan T. Chlebowski said at the San Antonio Breast Cancer Symposium.

"I think the good news for women here is that the risk rapidly dissipated in just a year or year and a half," said Dr. Chlebowski, a medical oncologist at the Los Angeles Biomedical Research Institute in Torrance, Calif.

The WHI was an extremely large National Institutes of Health-sponsored study on the prevention of cardiovascular disease and other chronic diseases. The HT clinical trial portion was halted prematurely in July 2002 upon detection of an increased breast cancer rate in its treatment arm.

In response to this announcement, the annual number of prescriptions for menopausal HT in the United States plunged from 60 million in 2001 to 25 million in 2003.

This development was temporally related to a sudden 8.6% decrease in the national annual age-adjusted incidence of breast cancer (20,000 fewer cases per year) beginning in 2003. The reduction has mostly affected the 50-to 69-year-old age group, and mostly has involved fewer estrogen receptor-positive tumors (N. Engl. J. Med. 2007; 356:1670-4).

Critics argued that this breast cancer decline might be an artifact resulting from less use of mammography once women stopped taking HT. But in San Antonio, Dr. Chlebowski presented two new analyses--involving a total of nearly 57,000 WHI participants--that ruled out a change in mammography utilization as a significant causal factor.