A new study led by investigators at Fred Hutchinson Cancer Research Center in Seattle may help explain why African-American women with breast cancer are more likely to be diagnosed with advanced disease and are less likely to survive the disease than white women.

In a large study of young African-American and white women in Atlanta, researchers at Fred Hutchinson and collaborators at Emory University and the Centers for Disease Control and Prevention have found that breast tumors from black women are more likely to be fast-growing and aggressive than those from white women.

The findings, published in the journal Cancer, hold true even for breast tumors of equally advanced stages in the two groups of women.

"One of the important conclusions from this study is that even when you correct for stage - that is, look at tumors of the same stage from white women and black women - tumors from the African-American women tend to have features characteristic of more aggressive and rapidly growing cancers," said Peggy Porter, M.D., lead author of the study and an associate member of Fred Hutchinson's Human Biology and Public Health Sciences divisions.

"If their tumors tend to grow more quickly, this may help to explain why their cancers are being diagnosed at later stages, which can lead to poorer outcomes," Porter said.

Other studies have reported similar findings, but the Fred Hutchinson analysis, funded by the National Cancer Institute and the Avon Foundation, is the first to examine tumors for a full array of proteins that control how quickly a cancer cell divides. Porter and colleagues found that tumors from African-American women were more likely to contain abnormal amounts of several cell-cycle regulatory proteins compared to tumors from white women. While the researchers do not yet know if these differences affect a woman's survival from cancer, cancers that lose control of these cell-cycle proteins tend to be more aggressive and harder to cure.

For nearly all factors analyzed, the researchers identified race-specific differences among the cancers, and tumors from African-American women almost always exhibited more aggressive characteristics than those from whites. For example, 13 percent of white women had stage III or higher disease, while nearly 20 percent of African-American women had this level of advanced disease. The odds of having a high-grade tumor, an indication of aggressiveness as judged by microscopic examination of the cells, was more than five times higher for black women than for white women.

Multiple studies have identified social, economic and cultural factors that contribute to later-stage diagnosis and poorer survival of breast cancer among African-Americans, but less is understood about differences in tumor biology that factor into this health disparity. The findings from the Fred Hutchinson study lay the groundwork for future studies to identify the specific risk factors that cause tumors from African-American women to develop dangerous characteristics, which could lead to new strategies to prevent and treat the disease.

"We know that African-American women with breast cancer are diagnosed at later stages, which is undoubtedly due in large part to socioeconomic factors, such as access to medical care. What we don't know is how much tumor biology contributes to diagnosis at later stages," Porter said. "We've just begun to tease out the biological factors that might contribute to late-stage diagnosis."

SOURCES:
Cancer, June 15, 2004
Fred Hutchinson Cancer Research Center (http://www.fhcrc.org)