Two Patterns Account for Drop in U.S. Breast Cancer Rates

Study suggests mammography saturation, drop in hormone replacement therapy played role

FRIDAY, May 4 (HealthDay News) -- Mammography saturation and a decrease in the use of hormone replacement therapy may be two factors that account for the decline in U.S. breast cancer rates observed since 1999, according to study findings published online May 3 in Breast Cancer Research.

Ahmedin Jemal, Ph.D., of the American Cancer Society in Atlanta, and colleagues analyzed 1975-2003 data from the National Cancer Institute's Surveillance, Epidemiology and End Results database.

The researchers found that age-specific rates of invasive breast cancer declined in all five-year age groups above age 45 between 1999 and 2003, and that rates sharply declined between 2002 and 2003. They attributed the 2002-2003 decline to a decrease in estrogen receptor-positive tumors among women aged 50 to 69. They also found that incidence rates for small tumors decreased by 4.1 percent per year from 2000-2003, and that incidence rates for localized disease decreased by 3.1 percent per year from 1999-2003.

"The rapidity of the decrease in breast cancer incidence rates after the dramatic reduction in the use of hormone replacement therapy…is not inconsistent with the relationship being caused by withdrawal of hormone replacement therapy," the authors write. "Sudden withdrawal of a promoting agent, such as hormone replacement therapy, could slow the growth of tumors that are below the detection limit of mammography and decrease incidence at least in the short term."

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