Decline in breast cancer incidence--United States, 1999-2003.

Breast cancer is the most commonly diagnosed cancer among females in the United States. The 2006 Annual Report to the Nation on the Status of Cancer described a stabilization in female breast cancer incidence rates during 2001-2003, ending increases that began in the 1980s, and a decline in the number of breast cancer cases diagnosed in 2003. In addition, researchers who used 1990-2003 data from the National Cancer Institute's (NCI's) Surveillance, Epidemiology, and End Results (SEER) program, representing approximately 14% of the U.S. population, reported a 7% decrease in invasive breast cancer rates from 2002 to 2003. To further assess breast cancer annual incidence rates during 1999-2003, CDC analyzed data collected by CDC's National Program of Cancer Registries (NPCR) and the NCI SEER program. These combined data account for approximately 86% of the U.S. population. The results of this analysis indicated that age-adjusted incidence rates for invasive breast cancer decreased each year during 1999-2003, with the greatest decrease (6.1%) occurring from 2002 to 2003; women aged > or = 50 years experienced a significant decrease during this period. Rates of in situ (i.e., noninvasive) breast cancer increased each year during 1999-2002 and then decreased from 2002 to 2003; women aged 50-79 years experienced a significant decrease during this period. Future studies should focus on determining potential causes for these decreases.