There had been a recent, rapid decline in postmenopausal hormone therapy use since 2002 when it 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.
It was unclear whether the drop was related to the decline in hormone therapy use or a decrease in mammography screening over the same period.
The study was conducted by a team of researchers led by Karla Kerlikowske at the University of California, San Francisco.
As part of the study researchers 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 was the first study to investigate breast cancer incidence and hormone therapy use in a population of women undergoing routine mammograms.
The study found that the use of hormone therapy among the study population declined by 7 percent a year between 2000 and 2002 and 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 wrote.
The findings of the study were published in the Journal of the National Cancer Institute.