In 2003, breast cancer incidence in the United States dropped sharply, and this decline may largely be due to the fact that millions of older women stopped using hormone replacement therapy (HRT) in 2002, according to a new analysis led by researchers at The University of Texas M. D. Anderson Cancer Center.

At the 29th annual San Antonio Breast Cancer Symposium, the investigators report that there was an overall 7 percent relative decline in breast cancer incidence between 2002 and 2003, and that the steepest decline - 12 percent - occurred in women between ages 50-69 diagnosed with estrogen receptor positive (ER-positive) breast cancer. This is the kind of breast cancer that is dependent on hormones for tumor growth.

From this, the researchers conclude that as many as 14,000 fewer women were diagnosed with breast cancer in 2003 than in 2002, a year in which the American Cancer Society estimates 203,500 new cases of breast cancer were diagnosed.

"It is the largest single drop in breast cancer incidence within a single year I am aware of," says Peter Ravdin, M.D., Ph.D., a research professor in the Department of Biostatistics at M. D. Anderson.