Sustained lower rates of breast cancer in the United States

Abstract

We have previously reported that, a sharp decrease in breast cancer incidence rates had occurred in 2003 among women C50 years of age in the United States [1]. This decrease seemed temporally related to a decrease in the use of hormone replacement therapy. In this update (Fig. 1) we report that, this decrease has been maintained into 2005. Comparing incidence from years 2000 through 2002 to years 2003 through 2005 significant decreases of 12.0% (se 0.8) and 7.8% (se 1.0) are seen for women 50–69 and [70 years of age, respectively. No significant decrease occurred in women less than 50. This reanalysis using the most recently released data from SEER [2] shows that, the decrease occurred primarily in ER positive breast cancers, with the rate of ER positive breast cancer in women 50– 69 years of age decreasing 14.5% and ER negative breast cancers decreasing 2.1%. Because the SEER data does not include information about the use of mammography or hormonal therapy by individual patients, we are unable to unambiguously attribute the decrease in breast cancer rates to a decrease in the use of hormonal therapy. However, other epidemiologic studies have reported decreased breast cancer incidence after a decrease in the use of hormone therapy in settings where there were no significant changes in screening mammography, suggesting that a change in screening mammography is unlikely to be the cause of the decrease [3, 4]. The women’s health initiative combined hormone therapy trial recently reported results for women stopping combined therapy, and a clear decrease in breast cancer rates was not seen [5]. Thus, the etiology of the sudden drop in ER positive breast cancer in the general population is unclear, but it has clearly occurred and has been maintained.