The incidence of new breast cancer cases in the US dropped a dramatic 7% between 2002 and 2003, researchers reported Thursday at the San Antonio Breast Cancer Symposium. That translates to about 14,000 fewer women who got the disease in 2003, say doctors from the University of Texas M.D. Anderson Cancer Center.

The reason, they think, might be that a significant number of women stopped using hormone replacement therapy (HRT) in 2002 after a well-publicized study was released that linked a certain type of HRT to a higher risk of breast cancer. That study, the Women's Health Initiative, found that HRT with estrogen and progestin -- commonly prescribed to help relieve symptoms like hot flashes in women going through menopause -- can significantly increase the risk of breast cancer. Soon after those results were announced, about half of the women using estrogen/progestin HRT stopped, according to researcher Peter Ravdin, MD, in a statement released by M.D. Anderson.

But he and other researchers say it's too soon to know for sure if that reduction in HRT use was the reason so many fewer cases of breast cancer were diagnosed the following year.

"Something went right in 2003, and it seems it was the decrease in the use of hormone therapy, but from the data we used we can only indirectly infer that is the case," Ravdin said in the statement.

American Cancer Society deputy chief medical officer Len Lichtenfeld, MD, says the decline in hormone use may have slowed the growth of cancers that already were in development. But there could be other explanations for the lower breast cancer rate, too.

"We were already seeing a slight decrease in the number of cancers year to year before the WHI study," he explains. "This could be due to lifestyle changes or some other unknown factor, but when you consider that this country doesn’t appear to be getting healthier, that raises the concern that there may have been some other explanation for that decrease. Examples could be fewer mammograms in general, and in particular for the increasing number of uninsured or underinsured women, or perhaps because of decreased access to mammogram facilities."

Women should not become complacent about getting screened for breast cancer, he warns.

"We recommend that a woman at average risk age 40 and over have a mammogram and clinical breast examination annually," he says. "If you are a post-menopausal woman who either stopped taking hormones or never took hormones, please do not delude yourself into thinking you don't need a mammogram."

As for taking hormone therapy, the recommendation remains: If you need it, take the lowest dose possible for the shortest time possible.