Mortality from prostate cancer is two to three times greater among African-American men between the ages of 40 and 70 years than among similarly aged American Caucasian men. The reasons for this disproportionately high mortality in African-American prostate cancer patients are unknown, but many studies have demonstrated that African-American men present with more advanced tumors.[2-6]
The definition of the African-American "race" is unclear. There is no genetic definition of race and there is clearly phenotypic heterogeneity among the US population of African-Americans. However, there is perhaps a common denominator among this group: Evidence indicating a greater percentage of bioactive lipids in the biologic systems of African-Americans suggests that they consume a diet high in fat content or one prepared utilizing fatty substances. Recent data demonstrate a strong association between prostate cancer progression and a high-fat diet.
Thus, this article will discuss African-American men as an ethnic/racial group and contrast this group with American Caucasian men. It will also review epidemiologic and histologic features of prostate cancer in these two distinct populations, as well as clinical and biologic factors. Finally, the implication of these findings will be discussed, as well as fertile areas for future research.
Currently, the clinical incidence of prostate cancer is 30% to 50% greater among African-American men than American Caucasian men. However, recent autopsy studies have demonstrated no statistical difference between the two races in the prevalence of the latent form of this cancer. Furthermore, one such study revealed that, among patients with latent cancer who were under age 50, there were no significant differences between the two races with regard to histologic differentiation, volume, multifocality, or anatomic distribution. Finally, the age of initiation of latent prostate cancer did not differ between African-American and American Caucasian males.
However, another study found that high-grade prostatic intraepithelial neoplasia was more prevalent and more extensive at an earlier age among African-American men than among their American Caucasian counterparts. The presence of high-grade prostatic intraepithelial neoplasia is closely associated with more aggressive prostate cancer. It has been hypothesized that high-grade prostatic intraepithelial neoplasia may be a precursor to clinically significant prostate cancer.
If this is true, it may account for the increased incidence and more advanced stage of prostate cancer among African-American men that has been reported by several investigators.[1-6] In 1993, the lifetime risk of being diagnosed with prostate cancer was 1 out of 11 for African-American men vs 1 out of 9 for American Caucasian men. In 1996, those lifetime risks have changed to one out of five for both populations.
In addition, Taylor and colleagues demonstrated that, from 1972 to 1991, prostate cancer diagnosis increased by 100% in American Caucasian men but by only 40% in African-American men. They reasoned that American Caucasian men are more likely to take part in early detection programs, and thus, are more likely to be diagnosed with prostate cancer than are African-American men. This study also demonstrated stage shifting; ie, men participating in early detection are more likely to be diagnosed at an earlier stage.
Several investigators have reported a lack of participation by African-American men in early detection programs for prostate cancer.[14-16] If this trend continues, one can only assume that the difference in stage presentation between ethnic groups will widen.
The lifetime risk of dying from prostate cancer is 3% for American Caucasian men and 4% for African-American men. Recently reported age-adjusted, age-specific mortality statistics demonstrate that death rates from prostate cancer are two to three times worse among African-American men than among American Caucasian men (40 to 70 years old). These statistics lead one to pose the obvious question, is this difference secondary to a more rapidly growing prostate cancer among African-American men, as compared with American Caucasian men? Or is it the result of delayed diagnosis among African-American men, which would account for their more advanced prostate cancer at presentation?
Conflicting data on survival outcome have been reported. Surveillance, Epidemiology, and End Results (SEER) data indicate a worse survival outcome for African-American men, stage for stage, compared to American Caucasian men. Other investigators report no statistically significant survival difference between the two races, stage for stage.[17,18] When analyzed retrospectively, overall survival has demonstrated an "ethnic survival crossover" based on age: African-American men have a worse survival than American Caucasian men under age 65 but a better survival above this age. At present, the cause of this phenomenon is purely speculative.
Further investigation of survival outcome in the two ethnic groups needs to be performed. Such studies should include not only race as an independent variable but also age (stratified by decades). Thus, a bivariate analysis of survival outcome should be done, as opposed to a univariate analysis.
Although only a few investigators have examined characteristics of radical prostatectomy specimens relative to race, the data in these early studies are consistent. African-Americans present with a significantly greater percentage of positive surgical margins compared to Caucasians.[20,21]
Although the percentages of cancers with extraprostatic extension and seminal vesicle involvement are higher among African-American men present than among American Caucasian men, these differences are not statistically significant due to the small sample size. Interestingly, studies by Moul et al and Powell et al demonstrate similar rates of lymph node metastasis in the two races, but the number of patients identified is small. In fact, in the study of Moul et al, no African-Americans presented with lymph node metastasis.[20,21] The explanation for this finding is unclear, but perhaps patient selection is important.
The importance of prostate cancer volume as an independent prognostic factor continues to be debated among investigators. Nevertheless, an examination of this parameter in the cohort of Moul et al demonstrates a greater prostate cancer volume among African-Americans than among their American Caucasian counterparts. Sakr et al report a significantly greater prostate cancer volume in African-Americans, compared with American Caucasians, particularly in those with locally advanced prostate cancer. In patients with organ-confined prostate cancer, tumor volume was greater among African-American men than among American Caucasian men, but the difference was not statistically significant. Again, small sample size may have contributed to the lack of statistical significance.[Sakr W et al, unpublished data, 1996; and reference 20]
Histologic grade of prostate cancer in ethnic groups (African-American men and American Caucasian men) has been examined by a few investigators, and no racial difference in grade has been discerned. However, in all of the series, the majority of patients of both races examined had a pathologic Gleason score of 7 (out of 10).[20,21] This finding suggests that there may be no biologic difference between ethnic groups.
Each Gleason score is derived by adding the grade assigned to the most predominant architectural pattern of the tumor to the grade of the second most predominant pattern. Sakr et al have examined the components of Gleason score 7 (3 + 4 vs 4 + 3) and stratified these components by race. They report that African-American men have a greater percentage of 4 + 3 component in radical prostatectomy specimens than do American Caucausian men, whereas American Caucasians have a greater percentage of 3 + 4 component.[Sakr et al, unpublished data, 1996] These differences are particularly evident among younger patients ( 55 years of age or less). This means that a higher proportion of cancers in African-American men are poorly differentiated.
This finding suggests that prostate cancer exhibits more aggressive biologic behavior and more rapid growth among African-American vs American Caucasian men. Another possible explanation for this finding is a delay in diagnosis of prostate cancer among African-Americans.