It's a question that has long puzzled medical researchers. Why do African American men have the highest rates of prostate cancer in the world? This disease is the leading cancer diagnosed among all men in the United States, according to the National Cancer Institute. Yet black men are 35% more likely than white men to develop prostate cancer, and they are two to three times more likely to die of it.
Some experts believe social and lifestyle factors may cause this disparity. Perhaps black men see doctors less often, either for cultural or economic reasons, or eat unhealthful foods. Two recent studies, however, suggest that biological differences between blacks and whites may play a greater role than previously believed.
Harvard researchers in December published results from a 10-year study that tracked the incidence of prostate cancer within a group of more than 45,000 male doctors, pharmacists, optometrists and other health professionals. African Americans in this study were nearly twice as likely to develop prostate cancer. Yet all the men participating had similar incomes and educational backgrounds, meaning they probably ate similar diets and were likely to get regular medical checkups. The researchers interpreted this to mean that lifestyle probably had little influence on the risk of prostate cancer within this group of men.
However, the Harvard team did detect a genetic difference among the black men in their study. Proteins called androgen receptors on prostate cells were more likely to have a slight alteration in African American men. Androgen receptors bind with hormones such as testosterone, which promotes the growth of prostate cancer. According to the Harvard study, this variation in androgen receptors among blacks may help explain a small portion of their higher prostate cancer rates.
Another study reported last December, at a medical conference in San Francisco, may shed additional light on why prostate cancer is more common, and more aggressive, in African Americans. Researchers at Louisiana State University studying prostate tumor samples noticed that those from black men tended to have far more blood vessels.
"We began asking questions," lead researcher Briana J. Williams said in a telephone interview from her office in Shreveport, La. Specifically, Williams and her team wanted to learn which genes encourage the growth of blood vessels around tumors, a process known as angiogenesis that's necessary for malignant cells to thrive. They also set out to determine which genes cause prostate tumors to metastasize, or spread elsewhere in the body.
After studying hundreds of genes, they turned up an unlikely suspect. In African American men, a gene that governs production of a protein known as TIMP-1 appears to work overtime. In Williams' study, tumor samples from blacks had more than 20 times the TIMP-1 as samples from whites. On the surface, that would seem to be an advantage, since low levels of TIMP-1 deactivate enzymes that promote the growth and spread of tumors.
But, explains Williams, "when TIMP-1 is so grossly over-expressed, it turns into too much of a good thing." At high levels, this protein appears to speed up the growth of blood vessels around tumors and the spread of malignant cells throughout the body. Not a good thing, indeed.
So why is TIMP-1 so high in black men? "I wish I had an answer," says Williams, who is director of basic urologic research at LSU Health Sciences Center. She has a few ideas, though. It may be that cholesterol in the diet triggers production of TIMP-1, she says. Besides their high risk of prostate cancer, black men are also somewhat more likely than whites to die of heart attacks, which are linked to high cholesterol levels. Men whose diets are rich in saturated fat, which raises cholesterol, are more likely to develop prostate cancer.
That's all rather intriguing, though Williams points out that it's much too soon to draw any conclusions about the role of TIMP-1 or cholesterol in the development of prostate cancer. She hopes that her research will lead to better methods for detecting the disease, and possibly even drugs to keep it in check.
Meanwhile, there's no downside to cutting back on saturated fat and watching your cholesterol, regardless of your race. Above all, ask your physician when you should start annual screening for prostate cancer. Public health agencies don't agree when men should begin getting checked, but most guidelines suggest no later than age 50.
African Americans--and guys of all races with a close relative (as in brother or father) who has had prostate cancer--should start getting screened earlier; the American Urological Assn. suggests age 40.
If you don't have health insurance, find out whether your community offers free or low-cost screening for prostate cancer; many do, particularly during September, which is Prostate Cancer Awareness month.
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Prostate Cancer and Race
(Rates per 100,000 men)
Asian/Pacific Islanders: 80.4
American Indian/Alaskan Natives: 49.6
Source: National Cancer Institute, based on data from 1990-1997.
Massachusetts freelance writer Timothy Gower is the author of "Staying at the Top of Your Game" (Avon Books, 1999). He can be reached by e-mail at email@example.com. The Healthy Man runs the second Monday of the month.