Drop in breast cancer incidence linked to hormone use, not mammograms

A recent decline in breast cancer incidence is unlikely to be caused by a decrease in mammography screening, according to a study published online August 14 in the Journal of the National Cancer Institute.

There has been a recent, rapid decline in postmenopausal hormone therapy use since 2002 when the Women's Health Initiative study found that hormone therapy was associated with an increased risk of breast cancer. Recent data has linked a decrease in breast cancer incidence over the last few years to this drop in hormone use, but this explanation remains controversial. Some researchers have said it is unclear whether the drop was related to the decline in hormone therapy use or a decrease in mammography screening over the same period.

Karla Kerlikowske, M.D., of the University of California, San Francisco and colleagues from the Breast Cancer Surveillance Consortium addressed this question by examining breast cancer rates in a population of women collected from seven mammography registries located in the U.S. who had received screening mammograms between 1997 and 2003. They collected data on over 600,000 mammograms performed on women ages 50 to 69. This is the first study to investigate breast cancer incidence and hormone therapy use in a population of women undergoing routine mammograms.

Between 2000 and 2003, use of hormone therapy among the study population declined by 7 percent a year between 2000 and 2002, then by 34 percent a year between 2002 and 2003. Over the same period, breast cancer incidence rates declined annually by 5 percent. Estrogen-receptor positive breast cancer rates fell by 13 percent each year from 2001 to 2003.

"Our results suggest that a decline in postmenopausal hormone therapy use has contributed to the decline in breast cancer incidence in the United States and that the small decline in screening mammography observed in the United States is unlikely to explain the national declines in breast cancer incidence," the authors write.