Prostate Cancer and African-American Men

May 1, 1997

Dr. Powell has written a comprehensive review of factors believed to contribute to the racial differences observed for prostate cancer incidence and mortality. Prostate cancer has a greater negative impact on African-Americans than on any other racial or ethnic group. However, the etiology of the striking racial variation in prostate cancer incidence and mortality remains enigmatic.

Dr. Powell has written a comprehensive review of factors believed tocontribute to the racial differences observed for prostate cancer incidenceand mortality. Prostate cancer has a greater negative impact on African-Americansthan on any other racial or ethnic group. However, the etiology of thestriking racial variation in prostate cancer incidence and mortality remainsenigmatic.

Although it is now accepted that cancer is the result of a series ofgenetic alterations,[1] prostate carcinogenesis appears to be heavily influencedby environmental factors as well. Moreover, socioeconomic factors contributesignificantly to the prostate cancer survival disadvantage experiencedby African-American men. Racial differences in prostate cancer incidenceand mortality are likely to be due to a complex interplay of genetic andenvironmental factors. Consequently, defining the etiology of these racialdifferences will be an imposing task.

Two Important, Unresolved Questions

With regard to race and prostate cancer, two important but separatequestions need to be resolved. The incidence of clinically manifest prostatecancer is higher in African-American men than in any other ethnic or racialgroup. However, the prevalence of candidate prostate cancer precursor lesions(prostatic intraepithelial neoplasia and incidental prostate cancer) isvery similar when African-American men are compared to other ethnic andracial groups.[2] This suggests that cancer-initiating events occur withuniform frequency regardless of race, while cancer-promoting events occurmore frequently in African-American men.

Alternatively, African-American men may be subjected to peculiar environmental,genetic, or epigenetic events that carry a greater risk for prostate cancerprogression. Factors that may explain the observed prostate cancer racialdifferences include dietary fat content and racial differences in androgenmetabolism. In addition, there may be unidentified molecular genetic factorsthat differentiate prostate cancer in African-Americans from that seenin other racial groups.

Dietary Fat and Prostate Cancer

Numerous studies have examined the relationship between dietary fatintake and prostate cancer. Several animal and in vitro studies have linkeddietary fat intake with prostate carcinogenesis.[3-5] Whereas case-controlstudies commonly demonstrate a link between dietary fat intake and prostatecancer risk,[6,7] cohort studies, which are thought to provide a more directindication of disease risk, do not consistently establish such a link.[8-11]

There is no clear mechanism linking dietary fat to prostate carcinogenesis.However, as pointed out by Dr. Powell, the large body of evidence implicatingdietary fat as an etiologic factor in this disease argues for further studyin this area. Moreover, studies showing that dietary fat intake is higherfor African-Americans than for other racial groups imply that dietary fatintake may contribute to racial differences in prostate carcinogenesis.

Role of Circulating Androgens

Similar to dietary fat intake, the role that circulating androgens playin prostate carcinogenesis has not been fully elucidated. Nevertheless,a considerable body of evidence points to androgens as possible risk factorsfor prostate cancer. Prostate cancer is essentially nonexistent in mencastrated before puberty.[12] Prolonged androgen stimulation of Noble ratsresults in the development of tumors in the dorsal lobe of the prostate.[13,14]

Based on this evidence, it has been hypothesized that elevated circulatingandrogen levels contribute to the development of prostate cancer. Moreover,circulating androgen levels, as well as 5-alpha-reductase levels, are higherin African-American men than in Caucasian and Asian men, suggesting thatandrogen levels may contribute to the racial differences that have beenobserved for prostate cancer incidence and progression.[15,16]

Thus, while precise roles have not been determined, both dietary fatintake and hormonal factors should be evaluated further to determine whetheror not they can shed light on the racial differences in prostate cancerincidence.

Socioeconomic Factors and Survival

Whether or not striking racial differences exist for prostate cancersurvival, stage for stage, is a point of controversy. A number of studieshave shown that, stage for stage, African-Americans are at a survival disadvantage.[17,18]However, considerable recent and historical evidence suggests that thisis not the case.[19-22] These data support the hypothesis that socioeconomicfactors account for the striking racial differences in prostate cancersurvival.

Dr. Powell discusses the impact that barriers to health care can haveon stage at presentation and subsequent prostate cancer survival. Numerousobstacles, including lack of prostate cancer education, avoidance behaviors,fear and incertitude about major medical centers, and limited medical resources,must be overcome to eliminate the effect of socioeconomic factors on racialdifferences in prostate cancer survival.

Summary

The impact that prostate cancer has on the African-American communityis unrivaled in any other racial or ethnic group. Several areas of researchmust be pursued in order to reduce prostate cancer mortality in the African-Americancommunity. The role of diet and hormones in prostate carcinogenesis mustbe elucidated. Also, the clinical and molecular characteristics that distinguishprostate cancer in African-American men require further investigation.[23-28]The multidisciplinary approach to these problems proposed by Dr. Powellseems to be a prudent, rational road to follow if we are to relieve theburden that prostate cancer represents for the African-American community.

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