THURSDAY, Sept. 23 (HealthDay News) -- A decline in breast cancer rates among postmenopausal women in Canada earlier this decade coincided with a decrease in the use of hormone replacement therapy, a new study shows.

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."

The largest decrease in hormone therapy occurred between 2002 and 2004, when use fell from 12.7 percent to 4.9 percent. During that same period, there was a 9.6 percent decline in breast cancer incidence, said Prithwish De, of the Canadian Cancer Society, and colleagues.

Their study appears online Sept. 23 in the Journal of the National Cancer Institute.

The drop in breast cancer incidence "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 decreased dramatically in several countries after the release in 2002 of a U.S. study that showed the health risks of hormone therapy outweighed the benefits.

The researchers noted that breast cancer rates among postmenopausal women in Canada began to rise again in 2005. This may be further evidence of a connection between hormone therapy and breast cancer, they said.

"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 thought to act as a promoter, rather than a cause of breast cancer," the researchers said in the release.

More information

The U.S. National Institute of Child Health and Human Development has more about hormone replacement therapy.