The differences in breast cancer rates among various racial and ethnic groups can be largely explained by the presence of breast cancer risk factors, according to a report in the Journal of the National Cancer Institute.

After factoring in age, breast cancer rates for women in racial or ethnic minority groups appear to be substantially lower than those for white women, the authors explain, but the influence of breast cancer risk factor distribution on these differences has received scant attention.

Dr. Rowan T. Chlebowski from Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Torrance, California, and colleagues examined whether recognized breast cancer risk factors could explain the difference in breast cancer rates between white women and women in minority groups.

White women had higher rates of mammography screening than other ethnic or racial groups, the report indicates, and, after factoring in age, breast cancer rates were higher for white women than for African Americans, Hispanics or Asian/Pacific Islanders.

After considering other breast cancer risk factors, such as number of close relatives with breast cancer; age at first menstruation, first birth and menopause; and prior breast biopsy for benign breast disease, the difference remained significant only for African-American women.

Although tumor type, size and disease stage did not differ significantly by ethnicity or race, the authors report, African-American women had significantly lower rates of estrogen receptor-positive tumors and a higher rate of estrogen-receptor-negative tumors than other minority women or white women.

Nearly one third of all breast cancers in African-American women were estrogen-receptor-negative and high grade, a rate nearly five-fold higher than in white women.

The higher rate of poor-prognosis breast cancer in African American women contributes to their increased risk of dying from breast cancer, which is unrelated to access to health care or mammography, the investigators explain.

In fact, the researchers note, the risk of death after breast cancer in African American women remained 79-percent higher than that in white women after factoring in age, body mass index and tumor stage.

“The results of this study indicate that differences in breast cancer incidence rates between most racial and ethnic groups can be largely explained by difference in risk factors except in African American women,” the authors conclude.

Cancer specialists “should be made aware of the high risk of poor-prognosis cancers in blacks,” Chlebowski told Reuters Health.

“The public health message stays pretty much the same,” Chlebowski concluded. However, “blacks probably should follow screening guidelines closely, since they are at risk of faster growing cancers.”

SOURCE: Journal of the National Cancer Institute, March 16, 2005.