Black women, regardless of age or body weight, have a threefold greater risk of developing a particularly aggressive type of breast cancer, compared with non-black women, Boston-based researchers report.

This type of breast cancer is more deadly, in part, because it does not possess receptors for the hormones estrogen or progesterone, nor a protein called HER2. This means that women with these “triple-negative tumors” cannot be helped by drugs that target estrogen and progesterone - including tamoxifen and aromatase inhibitors - or by the anti-HER2 therapy Herceptin.

“The higher prevalence of triple-negative breast tumors in black women in all age and weight categories likely contributes to black women’s unfavorable breast cancer prognosis,” Dr. Carol Rosenberg from Boston University School of Medicine noted in comments to Reuters Health.

“The reasons explaining this finding are not certain, but it is possible that black women may be at intrinsically greater risk of these more aggressive tumors,” she added.

Rosenberg and colleagues studied 415 women with breast cancer. Thirty-six percent of the women were white, 43 percent were black, 10 percent Hispanic and 11 percent of “other” races. Forty-seven percent of the women were obese.

Most of the breast tumors (72 percent) were estrogen receptor-positive and/or progesterone receptor-positive; 20 percent were triple-negative and 13 percent were HER2-positive.

The investigators focused on triple-negative tumors, which are associated with poor prognosis, and found that the odds ratio for having this tumour type was threefold greater for black women compared with white women.

Triple-negative tumors made up equal fractions - roughly 30 percent - of breast cancers in younger and older black women and in obese and non-obese black women, according to the team’s report published online March 25 in the journal Breast Cancer Research.

“It was known previously,” Rosenberg commented, “that premenopausal black women had more triple-negative tumors. However, there were no previous data about weight. What we found that was new was that these tumors were just as common in black women diagnosed before or after age 50, and in those who were or were not obese.”

The investigators conclude, “Other factors must determine tumor subtype.”

SOURCE: Breast Cancer Research, 2009.