UW-Madison study ties lower hormone use to fewer breast cancer cases

Decreased use of post-menopausal hormones likely accounts for more than 40 percent of a dramatic, one-year decline in breast cancer incidence, according to a new analysis by University of Wisconsin–Madison cancer researchers.

The analysis, the first of its kind to measure the effects of hormone therapy cessation on breast cancer incidence, is being presented this week at the American Association for Cancer Research Frontiers in Cancer Prevention Research Conference in Houston.

The findings by Brian Sprague, a postdoctoral fellow at the UW Carbone Cancer Center, estimate that 42 percent of the decline of breast cancer incidence nationally from 2002 and 2003 may be linked to cessation of hormone replacement therapy (HRT) following the Women’s Health Initiative clinical trial results that showed HRT causes an increased risk of both breast cancer and cardiovascular disease in some women.

“The number of breast cancer cases rose steadily from 1998 to 2002 followed by a dramatic, seven percent drop in 2003. Since 2003, breast cancer incidence has remained constant. So the possible connection between breast cancer rates and hormone use was an intriguing question based on the timing,” says Sprague.

Sprague says the decline in use of HRT led to approximately 6000 fewer cases of invasive breast cancer in the year following announcement of the landmark clinical trial results. It’s estimated that use of hormones has dropped by about 75 percent since 2002.

“We used a simple mathematical model that took into account the increased risk of breast cancer associated with hormone use and the number of women who stopped using hormones after the Women’s Health Initiative results were published.” said Sprague.

The researchers considered a range of scenarios and found that under all reasonable ones, the reduction in hormone use explained a big portion of the incidence decline, but not all of it.

Sprague and co-authors Dr. Amy Trentham-Dietz and Dr. Patrick Remington say it is unclear to what extent other factors may have contributed to the decline, including screening and early detection, and a falling number of late-stage breast cancer cases.

The results mean that the Women’s Health Initiative study was helpful in reducing breast cancer incidence, according to Sprague.  But he cautions that the decision to use postmenopausal hormones is a personal one which should be made by each woman in consultation with her doctor.

“Our study should not affect women currently on hormone therapy.  But the study is useful for improving understanding of population trends in breast cancer incidence,” says Sprague.