Studies have shown that African-American women have significantly higher death rates from breast cancer than any other ethnic group. Lower screening levels, inadequate access to health care, and certain lifestyle and environmental factors certainly play a role. But researchers at Howard University in Washington, D.C. believe there may be some distinct biological influences as well.

Dr. Indra Poola, a biochemist and molecular biologist at Howard, led a team of researchers that focused on the composition of estrogen receptors, which apparently differs among women of different racial and ethnic backgrounds. Writing in the journal Cancer, they speculated that this difference may influence how fast breast tumors grow-and thus make them more difficult to treat depending on their cellular concentrations.

"Several cancer surveys have shown that African-American women develop highly aggressive breast tumors and experience about three times higher mortality rates compared with other populations," they wrote. "The data presented here show for the first time that functionally active ER [estrogen receptor] profiles in the breast tumors of African-American women are different from those in Caucasian women."

Estrogen receptors are proteins on cell surfaces that bind to estrogen. All normal breast cells have estrogen receptors; however, when cancer cells have them, estrogen can feed their growth. Certain drugs such as tamoxifen block the interaction between estrogen and estrogen receptors.

There are four types of estrogen receptors, called isoforms. Poola's team and other researchers believe that the growth of a breast tumor may depend on which of these isoforms are present on a cell, and in what concentrations. To test their theory, they studied breast tumors samples from 24 African-American women and found that the levels of two of these isoforms were significantly different in African-American women.

Specifically, Poola's team found that African-American women had fewer of the "protective" ERb isoform and elevated levels of the cancer-stimulating ERa exon 5 isoform.

"Variations in estrogen-mediated signaling because of the alternations in these two ER isoforms may account in part for differences in tumor biology between African-American women and Caucasian women," they concluded.

They suggested that an understanding of these biological differences may be important for developing specific drugs and treatment strategies targeted at African-American women.

SOURCE:
Cancer, February 1, 2002; 94:615-623