SAN ANTONIOReversing a decades-old trend, the incidence of invasive breast cancer dropped dramatically in 2003, relative to 2002, possibly a result of postmenopausal women discontinuing hormone replacement therapy (HRT) due to breast cancer concerns, Peter M. Ravdin, MD, PhD, of M.D. Anderson Cancer Center, reported at the 29th Annual San Antonio Breast Cancer Symposium (abstract 5).
The analysis found an overall 7% reduction in invasive breast cancers. The decrease was evident only in women older than age 50, and primarily for estrogen-receptor (ER)-positive tumors. A steep 12% decline was noted for women aged 50 to 69; there was a trend toward a decline for women over 40, and for the subgroup aged 40 to 49.
The data were based on incidence data from the Surveillance Epidemiology and End Results (SEER) database. The analysis also involved investigators from the National Cancer Institute.
Whereas the age-adjusted incidence of breast cancer for all women, irrespective of age, was 185/100,000 women/year in 2000, and nearly this high in 2002, it dropped to 170/100,000 women/year in 2003. The effect may represent up to 14,000 cases per year, Dr. Ravdin said.
The difference was so astounding that investigators questioned whether the numbers were "real," he said, but the fact that all nine SEER registries documented the decline convinced them it was. The SEER registry program will not release its 2004 data until 2007.
The leading causes of this decline were considered to be changes in mammographic screening and changes in the use of HRT, both of which would be expected for women older than 50. Since the relative reduction was approximately twice as large for ER-positive tumors as ER-negative tumors, investigators presumed "something important is going on biologically," as opposed to improvements in detection, Dr. Ravdin maintained. The use of mammography from 2000 to 2003 has changed very little and, in fact, has actually decreased by 1% among women aged 40 and older and by 3% among women aged 50 to 69.
Instead, investigators noted that the reduction in breast cancers corresponded to the report from the Women's Health Initiative in July 2002 that found a 1.24-fold higher breast cancer risk for combined estrogen plus progestin HRT. This report triggered a 50% or so decrease in the use of HRT within 6 months, he said.