Prostate cancer is a major health-care problem for African-American men. The age-adjusted incidence of prostate carcinoma in African-American men is approximately 50% greater than in white men. Furthermore, studies (1–3) have consistently demonstrated that the mortality rate from prostate cancer is significantly greater in African-American men than in white men. This fact remains true, even after adjustment for stage at presentation (2). Some researchers have speculated that variable access to health care may substantively contribute to the disparate prostate cancer survival between racial groups. Robbins et al.(3) recently reported on survival from prostate carcinoma in participants in a large health-care maintenance organization in which one would assume that prostate carcinoma was detected and treated similarly in all races. In that study, the death rate from prostate cancer was higher in African-American men than in white men after adjustment for age and stage. These epidemiologic observations have led to the hypothesis that prostate carcinoma in African-American men is more biologically aggressive than in white men. To investigate whether this difference is due to tumor biology or epigenetic factors, we have used high-density tissue microarray technology, developed by Kononen et al.(4). Tissue microarrays can contain up to 1000 tissue samples and can be used for multiple studies, thereby conserving tissue and assuring the uniformity of test conditions.

Our aim was to create a collection of clinically matched tumor samples from African-American and white men with prostate carcinoma and to investigate potential differences in tumor proliferation between the two groups. We matched African-American and white men before surgery by serum prostatespecific antigen (PSA) levels and fineneedle biopsy Gleason scores to identify men who presented with similar clinical features, so that any biologic differences identified could be attributed to race. The biomarker selected for this study was the proliferation marker Ki-67. Ki-67 is a nuclear protein that is expressed in G1, S, G2, and M phases of the cell cycle but is not detected in cells in G0 phase (5). We defined the Ki-67 labeling index as the percent nuclear area stained with Ki-67 (6). Previous studies (7–9) of prostate cancer have described consistent associations between the Ki-67 labeling index and the Gleason grade (ie, tumor grade).