Age is the biggest risk factor for developing prostate cancer; more than 75% of men diagnosed with prostate cancer are over age 65. In theory, ethnicity should be independent of such statistics. But the disease disproportionately affects African-American men, who, along with black Jamaican men, have the highest prostate cancer incidence rates in the world.
A study in this issue of the Journal (see article, p. 388) looked at factors such age, insurance status, income, and prostate-specific antigen level to try to explain why African-Americans have twice the risk of non-Hispanic whites of presenting with advanced-stage prostate cancer. The results showed that no single element that could explain the differences.
"Even if you account for the fact that theres a differential distribution of socioeconomic resources and even if you account for other clinical factors or characteristics of the tumor, . . . you cant explain away the discrepancy between whites and blacks with respect to advanced-stage diseases," said Arnold L. Potosky, Ph.D., of the Division of Cancer Control and Population Sciences at the National Cancer Institute and one of the studys co-authors.
Led by Richard Hoffman, M.D., of the Department of Veterans Affairs Medical Center at the University of New Mexico, researchers evaluated the possible association between race/ethnicity and advanced-stage prostate cancer by obtaining medical abstracts and other information from 3,173 men with prostate cancer. Specifically, they recorded information on race/ethnicity, age, marital status, insurance status, educational level, household income, employment status, comorbidity, urinary function, prostate-specific antigen level, tumor grade, and clinical stage.
The study acknowledges that demographic characteristics, socioeconomic status, and comorbidity may limit cancer screening in African-Americans and contribute to delayed diagnosis. However, the authors were surprised that some factors and situations were not more influential.
"Whats surprising is that if you believe these discrepancies are due to differential access to care or somehow theres a discrimination in the medical care system it seems unlikely based on our study," said Potosky. "I thought that by accounting for these factors we would reduce the relative risk closer to one than we did between whites and blacks."
Diet?
Another recent study looked at several dietary and lifestyle factors as possible reasons for differences in incidence rates. Elizabeth Platz, Sc.D., an assistant professor in the Department of Epidemiology at the Johns Hopkins School of Hygiene and Public Health, Baltimore, evaluated 45,410 male health care professionals and found that the African-American participants had a 1.7 times greater risk of prostate cancer than the white participants.
Upon closer examination, Platz found that, compared with white men, the African-American men in her study had lower intakes of saturated fat and calcium and higher intakes of fructose and consumed fewer tomato products. After taking into account the differences in the distribution of these factors, African-American men still had an incidence rate that was almost twice as high as white men.
Platz said that socioeconomic status, which is cited by many researchers as a barrier to screening and proper health care, was unlikely to be a factor in this study. All the men studied were pharmacists, optometrists, veterinarians, or other health care professionals. Platz maintains that there are many possibilities why diet and lifestyle factors did not explain the higher rate.
Biology?
"It is possible that . . . emerging [risk or protective] factors or yet unidentified prostate cancer risk factors may vary between racial groups," Platz said. She also noted that the study measured dietary and lifestyle factors in adulthood; exposures to these factors early in life may be more important.
"There is good evidence to suggest that prostate cancer develops more rapidly in African-American men, leading to a higher likelihood of aggressive disease at an early age," said Peter Gann, M.D., Sc.D., of the Department of Preventive Medicine at Northwestern University Medical School. "This supports the concept that prostate cancer is inherently more aggressive in African-American men than in whites."
Similarly, Hoffmans study suggested that future research take a closer look at possible racial differences in tumor biology as a way of explaining the discrepancies.
"We should try and understand the changes that go on in the tumor and see if there are factors that might identify more aggressive tumors in a reliable and consistent way," said Janet L. Stanford, Ph.D., member and research professor at the Fred Hutchinson Cancer Research Center and one of the studys co-authors.
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One such study considering the theory that African-Americans have more aggressive disease looked at two groups of men, one white, one African-American, to determine if the same treatment was equally effective. Philip P. Connell, M.D., and colleagues at the University of Chicago and the University of Illinois studied 418 African-American patients and 475 white patients who received conformal radiotherapy. The study took into account that African-Americans are more likely to present with advanced stage disease at a younger age. However, after adjusting for various factors, the study found that conformal radiotherapy was equally effective in African-American and white patients.
Despite this and other research that indicates African-Americans and whites respond equally to certain treatments, many researchers cite evidence that the disease develops differently in African-Americans due to genetic and environmental factors.
"There have been some interesting reports suggesting that the HPC1 gene is found in African-American prostate cancer families more than whites," said Timothy R. Rebbeck, Ph.D., an epidemiologist at the University of Pennsylvania School of Medicine. (The HPC1 gene has been shown to confer risk of prostate cancer. See related story, this page.) "There are some clues about variants in genes that differ by race and may be associated with prostate cancer risk. However, its early to say very much about how these relations will pan out."
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"We need to design prospective studies to examine variations in infancy, in childhood, teenage years, and in early adulthood," she said. "It could be that we have just missed the relevant moment for exposures that are important for racial differences in prostate cancer risk. . . . Money is earmarked for prostate cancer research; we just need to think more creatively about how to study the causes of this disease."
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