Genetic factors may play a significant role in the racial differences encountered in the epidemiology of breast cancer

Mar 14 2005

A new review finds similarities between the clinical presentation and course of breast cancer in Africans and African-Americans, suggesting that genetic factors may play a significant role in the racial differences encountered in the epidemiology of breast cancer in America.

The article, published in the April 15, 2005 issue of CANCER, a peer-reviewed journal of the American Cancer Society, also observes that Africa faces potential increases in breast cancer rates as African women adopt Western reproductive and dietary behaviors that have been shown to increase the risk of breast cancer.

Population studies show while African American women have lower rates of breast cancer than white women in the United States, they have poorer outcomes. African American women are also more likely to get breast cancer at a younger age, and among women in the U.S. under the age of 45, African Americans have the highest incidence rates. African Americans are also more likely to be diagnosed with higher stage disease – i.e., estrogen receptor-negative, high-grade tumors that are node-positive. This clinical pattern is similar to that identified in the Ashkenazi populations that led to the discovery of BRCA-1 and -2 gene mutations, prompting many scientists to speculate that there may also be a genetic component contributing to breast cancer in African Americans.

Alero Fregene, M.D. and Lisa A. Newman, M.D., M.P.H. of the University of Michigan Comprehensive Cancer Center conducted an extensive literature review of English-language studies of breast cancer in sub-Saharan Africa. They say understanding the breast cancer burden and clinical characteristics in sub-Saharan Africa, where the majority of African American trace their ancestry from, may contribute to the understanding of racial factors in breast cancer.

The review found current literature, while incomplete, particularly in tumor biology, genetics, and inheritance patterns, does demonstrate epidemiological and clinical similarities between Africans and African Americans. African women are diagnosed most often between 35 and 45 years, and more than fifteen years earlier than women in Europe and North America. The mortality rate seen among women in sub-Saharan Africa is disproportionately high compared to the incident rate, as in African American women. Their tumors tend to be very aggressive with short periods of time between the onset of symptoms and diagnosis. Moreover, the tumors at diagnosis also tend to be higher grade, often involving axillary lymph nodes and, therefore, higher stages disease with worse prognoses. Poor prognosis is compounded by resource poor healthcare infrastructure, which offers limited treatment options and underutilizes effective treatments.

Still, the incidence of breast cancer in sub-Saharan Africa is small at 20 per 100,000 compared to 90 per 100,000 people in the West. The reason for this geographic disparity has much to do with protective behaviors that inadvertently minimize estrogen exposure, such as reproductive patterns, body build, and dietary patterns. The authors say as Africans adopt Western lifestyles, these protective behaviors are expected to be replaced with known risk factors for breast cancer.

The authors conclude, "The parallels between African American and Sub-Saharan African breast cancer patients suggests the possible effects of hereditary factors, and these influences may cause the younger age distribution that is seen among these patient populations to persist."

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