FRIDAY, Feb. 19 (HealthDay News) -- Breast cancer rates are declining, especially among women over 50 who have estrogen receptor-positive tumors, and now a new study narrows down the reason why.
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After analyzing data on more than 350,000 women with breast cancer, Harvard researchers concluded that the decline may be linked with decreasing use of hormone replacement therapy -- and that association, in turn, may explain why the decline is especially evident among white, affluent women.
Those are the very women most likely to have used hormone replacement therapy, experts said, and to have stopped using it following the July 2002 release of the results of the Women's Health Initiative, a large national study that discovered an increased risk of breast cancer and heart disease with hormone replacement therapy.
The new study lends credence to the speculation about what's behind the decline. "Our study provides evidence to support the idea that the observed declines are due to the changing use of hormone therapy, by showing that the declines in breast cancer rates were sharpest among those women most likely to have received hormone therapy -- that is, affluent white women," said study co-author Jarvis Chen, a research scientist at the Harvard School of Public Health.
The new study was released online Feb. 10 and will be published in the April supplement of the American Journal of Public Health.
"We further showed that declines in breast cancer rates vary within racial/ethnic groups by socioeconomic position, and that the declines primarily affect rates of estrogen receptor-positive cancers," Chen said.
Lead study author Nancy Krieger, a professor in the department of society, human development and health at the Harvard School of Public Health, and her colleagues analyzed breast cancer data from the U.S. Surveillance, Epidemiology and End Result (SEER) database, stratified by race/ethnicity, county income level, age and estrogen receptor status of the tumor. The women had been diagnosed between 1992 and 2005.
The SEER database does not include individual socioeconomic information, Chen said. "To overcome this, we analyzed breast cancer rates in relation to the socioeconomic characteristics of the counties where the women lived," she explained.
"The recent decline in U.S. breast cancer incidence was not equally beneficial to all women, but instead mirrored the social patterning of hormone therapy use," the researchers concluded.
The silver lining? The fact that minorities and low-income women used hormone therapy less -- because of expense and less access to health care -- may have spared them from increases in breast cancer diagnoses, Chen said.
The new findings come as no surprise to Susan Brown, director of health education for Susan G. Komen for the Cure.
"We know there are ethnic differences in breast cancer incidence," she said. "African-American women are more likely to get breast cancer at an earlier age, and they are more likely to be diagnosed with breast cancer tumors that have molecular markers associated with a poorer prognosis."
ER-negative tumors, she said, are also more common in black women, and experts would not expect the rates of those tumors to be affected by discontinuing HRT use.
Brown brings up another factor that could be contributing to the trend: the declining rate of mammography screening. "We are hoping we aren't seeing a decline in incidence due to mammography screening rates being down," she said.
Copyright © 2010 HealthDay. All rights reserved.
SOURCES: Susan Brown, director, health education, Susan G. Komen for the Cure, Dallas; Jarvis Chen, Sc.D., research scientist, Harvard School of Public Health, Boston; Feb. 10, 2010, American Journal of Public Health, online
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