Explaining the Recent Decrease in Breast Cancer Incidence

A recent report of an unexpected decrease in U.S. breast cancer incidence from 2002 to 2003 generated much attention. The authors of that report suggested that the decrease resulted from the abrupt decline in use of menopausal hormone therapy following publication of initial Women’s Health Initiative (WHI) findings in July 2002 (N Engl J Med 2007; 356:1670). Now, American Cancer Society epidemiologists have examined temporal trends in invasive and in situ breast cancer in nine Surveillance, Epidemiology, and End Results (SEER) cancer registries from 1975 through 2003, focusing on age at diagnosis, tumor stage and size, and estrogen- and progestin-receptor status.

Overall, the incidence of breast cancer began to decrease in 1999. The incidenc…