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
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
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.
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