Breast cancer rates are declining, but some groups have seen a more significant decline than others, with race, ethnicity and economic background playing a part.
According to a new national study, the only significant decline in breast cancer rates occurred among white, non-Hispanic women, 50 and older, who live in affluent countries and who have the kind of tumors that an estrogen-rich environment will nourish. Breast cancer rates declined by as much as 10 percent annually in this group.
The study, which appears online and in the April supplement of the American Journal of Public Health, relied on data obtained from 13 U.S. population-based cancer registries for 1992 to 2005, and analyzed trends among 350,000 cases, looking at race/ethnicity and socioeconomic position, as well as age at diagnosis and breast cancer tumor characteristics.
In 2002, the Women's Health Initiative (WHI) study prompted many doctors to stop prescribing hormone therapy when the findings contradicted the previously held assumption that estrogen/progestin replacement therapy would lower a woman's risk of heart disease.
Instead, the findings suggested that hormone therapy actually would increase the risk of heart disease and breast cancer. Although the new study on breast cancer trends did not have access to information on individual women's hormone therapy use, the same group of women who exhibited the most significant decline in breast cancer rates was also the group most likely to have been taking hormones before the Women's Health Initiative.
"The fact that it was not a general decline gives further credence to the idea that it was something very specific commonly affecting this group of women," said lead study author Nancy Krieger, Ph.D. "It looks like the most logical thing was a change in the administration of hormone therapy. The rates didn't decline among white women living in less affluent countries or black women in rich or poor countries."
Krieger is a professor in the department of society, human development and health at the Harvard School of Public Health.
To Susan Brown, director of health education for Susan G. Komen for the Cure, these studies underline an important lesson. "The WHI study reminded us of the importance of having enough evidence. The idea that hormone therapy prevented cardiovascular problems relied on only one rigorous scientific study. If your doctor prescribes a treatment, you might want to ask, what do studies show, what is the evidence? Physicians should be prepared to answer these questions."
With any prescribed treatment, there are risks and benefits, Brown said. "To really make an informed choice, it's important to understand the risks."
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