After her research team analyzed the tissue samples and compared them with those of more than 900 Canadian women primarily of European descent, Olopade was amazed by the results. The tumors in the African women were very different, a whole other form of the disease. They often lacked estrogen receptors and were more likely to originate from the outer basal cells of the breast rather than the more usual inner milk-secreting luminal cells. A landmark study by researchers at the University of North Carolina-Lineberger Comprehensive Cancer Center in 2006 found that, remarkably, this basal-like "triple negative" subtype showed up in 39 percent of the study's premenopausal women who were African-American, compared with only 16 percent in those who weren't. A larger study published this summer in the journal Cancer confirmed that in the United States, black women overall are twice as likely to have triple negative tumors as white women. In general, this type of breast cancer has one of the worst survival rates. These findings help explain why young black women are more likely to get breast cancer early—10, 20, 30 years before menopause—and have nearly double the odds of dying from it.
What causes this aggressive cancer, and why would it affect one population more than another? One clue may be the BRCA1 gene. "Women who have mutations of this gene are at higher risk of getting breast cancer," says Ruth O'Regan, MD, associate professor of hematology and oncology at the Emory Winship Cancer Institute in Atlanta. "And that mutant gene also appears to play a role in these triple negative cancers. But exactly how is not clear."
Mary Jo Lund, PhD, research assistant professor at the Rollins School of Public Health at Emory, co-authored two studies of women in Atlanta to see whether economics plays a role in triple negative disease. "Even when we adjusted for socioeconomic status and delayed access to healthcare," she says, "black women were twice as likely as white women to have triple negative tumors. So it is not just about poverty. There appear to be true biological differences."
Still, she and other oncology researchers, including Olopade, who received a $500,000 MacArthur award in 2005 for her work, remain convinced that some interaction between genetics and the environment triggers the disease. As a result, some researchers are now exploring how prolonged stress—from factors like income deprivation, social isolation, and exposure to violence—may be altering the body's biochemistry to produce gene mutations.
Lund goes on to quote a colleague who said, "I can't help but think that if these prevalences had been seen in white women, we'd have already found new targeted treatments for these tumors." Asked if she believes that's true, Carolyn Runowicz, MD, past president of the American Cancer Society, counters, "It's not that researchers are dragging their feet. The technical ability to diagnose cancer subtypes like triple negative tumors has only emerged in the last decade." And many African-Americans may be wary of participating in clinical trials—a suspicion that dates back to the notorious Tuskegee experiment, in which 399 unwitting black men with syphilis were used as guinea pigs in a government-sponsored study. For 40 years beginning in 1932, researchers withheld treatment so they could study the progress of the disease, and many of the men died.