Researchers puzzling over why the decreased incidence of invasive breast cancer in the United States seen in 2002 and 2003 did not extend to women of African ancestry say that genetics may be behind the disparity. Presenting their findings at the 2008 annual meeting of the American Association for Cancer Research in San Diego, researchers from the University of Chicago Medical Center reported that while breast cancer incidence rates in women over 50 declined sharply during 2002 and 2003, the decline was confined to Caucasians. "The benefit was not equal across racial groups," said researcher Dezheng Huo. "Only Caucasians saw this reduced incidence of invasive cancers."
Much of the racial disparity, the researchers suspect, may have resulted from differences in biology. "We suspect," Huo said, "that the widespread discontinuation of menopausal hormone use had a greater effect on Caucasians." African Americans are less likely to use hormone replacement therapy and less likely to develop breast cancers that are receptive to estrogen, Huo explained, so they were harmed less by taking hormones and benefited less by discontinuing them.
African Americans had "a similar magnitude of reduction in hormone therapy use," he added, "yet it did not lead to any benefit, suggesting that genetic variations in estrogen and progesterone metabolism may play a role in how women of African ancestry respond to hormonal therapies."
Almost 80 percent of breast cancers in Caucasians are estrogen receptor positive, a type of tumor that depends on estrogen to grow, said Huo, compared to about 60 percent in African Americans. That proportion drops to about 30 percent among Nigerian women. "The finding that the rate of invasive breast cancer decreased suggests that estrogen serves as a promoter rather than an initiator of breast cancer," say the study authors.
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Source: University of Chicago Medical Center
