Black women diagnosed with breast cancer have a greater chance of dying from the disease than white women, according to a new study in the Journal of the National Cancer Institute.

Age-standardized breast cancer mortality rates in the U.S. have remained higher and declined more slowly among black women. This study was undertaken because the underlying causes of this disparity were unclear.

To explore this, Idan Menashe, Ph.D., of the Division of Cancer Epidemiology and Genetics at the National Cancer Institute, in Rockville, Md., and colleagues used the Surveillance, Epidemiology, and End Results program to investigate almost 250,000 women diagnosed with breast cancer from January 1990 through December 2003. Researchers calculated black-to-white ratios of mortality, incidence, hazard of breast cancer death (probability of dying from the disease), and incidence-based mortality, with some analyses stratified by oestrogen receptor (ER) status and age.

The researchers found a statistically significantly higher hazard of death in black women diagnosed with breast cancer compared to whites, especially in the first few years after diagnosis. Hazard rates of breast cancer death declined substantially for ER-positive tumours and modestly for ER-negative tumours but were persistently higher for blacks than whites.

“These differences in hazard may reflect racial differences in response and access to innovations in breast cancer treatment, as well as other biological and non-biological factors,” the authors write. “Hence, greater emphasis should be placed on identifying the reasons for these increased hazards among black women and on developing new therapeutic approaches to address the disparity.”

In another study, also published in this issue, Kathy S. Albain, M.D., of Loyola University Medical Center in Maywood, Ill., found that even when African American patients received the same care as all other patients, their survival rates were lower for breast, prostate and ovarian cancers, but were equivalent for all other major cancers.

Albain and colleagues analysed records of more than 19,000 patients who participated in phase III cancer clinical trials conducted by the Southwest Oncology Group. "Patients of all races had the same doctors and received the same state-of-the-art treatments," Albain said. "It was a level playing field for everyone. So our findings cast doubt on a widely accepted theory that African Americans' lower survival rates for certain cancers are solely due to such factors as poverty and poor access to quality health care."

Albain's study found no statistically significant association between race and survival for lung cancer, colon cancer, lymphoma, leukaemia, or myeloma.

The cancers that did show survival gaps -- breast, prostate and ovarian -- are gender-related and the survival disparity persisted after adjustment for treatment factors, tumour variables, and socioeconomic status. The findings therefore suggest that the survival gap for these cancers is most likely due to an interaction of tumour biologic factors, hormonal environment, and inherited variations genes that control metabolism of drugs, toxins and hormones, Albain said.

In an accompanying editorial, Otis W. Brawley, M.D., of the American Cancer Society, said results of the Albain et al. study provide evidence that racial differences in the U.S. for certain cancers can be attributed to unequal care. He points out that blacks are less likely to have disease detected early and less likely to receive adequate treatment when it is detected.

The Menashe et al. study, according to Brawley, showed clear differences in mortality by race.

“Taken together, the two studies and others do not suggest that blacks have a different kind of breast cancer, but rather that there are multiple kinds of breast cancer and a higher proportion of black breast cancer patients have the worse kinds,” the editorialist writes. “No race has a monopoly on the good kind, nor the bad kind of breast cancer, but the prevalences differ.”