Researchers analyzed national data and found that "the nearly 10 percent drop in invasive breast cancer rates coincided with the decline in use of hormone replacement therapy reported among Canadian women aged 50 to 69 years," according to HealthDay News.
The largest drop in hormone therapy's use occurred between 2002 and 2004, when use fell from 12.7 percent to 4.9 percent. During that same period, breast cancer rates dropped nearly 10 percent, according to Prithwish De, of the Canadian Cancer Society, and colleagues.
The drop in breast cancer rates "is likely explained by the concurrent decline in the use of hormone replacement therapy among Canadian women," the researchers said in a journal news release.
Hormone therapy use dropped off radically in several countries after a 2002 U.S. study showed that the risks of the treatment far outweighed the benefits.
The study authors noted that breast cancer rates among postmenopausal women in Canada began to rise again in 2005. They claim that this might be further evidence of a link between hormone therapy and breast cancer.
"Such a rebound might be expected if [undetected] hormone-sensitive tumors were merely slowed by the withdrawal of hormone replacement therapy rather than prevented by it. If so, hormone replacement therapy may be brought to act as a promoter, rather than a cause of breast cancer," the news release concluded.
