Racial differences in prostate cancer growth: Apoptosis and cell proliferation in Caucasian and African-American patients

BACKGROUND. Epidemiologic evidence reveals striking racial differences in i ncidence and clinical behavior of prostate cancer among American men. In th is study, we assessed the incidence of apoptosis and cell proliferation in prostate cancer specimens from African-American and Caucasian patients in a n attempt to identify potential differences in tumor growth determinants be tween the two ethnic groups. METHODS. Apoptosis and cell proliferation were analyzed in archival paraffi n-embedded prostatic tumors from 44 African-American and 35 Caucasian age-m atched men who underwent radical prostatectomy for localized prostate cance r. Both groups had comparable preoperative prostate-specific antigen (PSA) levels, clinical stage, and Gleason scores, and neither group of patients r eceived neoadjuvant therapy Frier to surgery. Apoptotic status in prostate tumors was evaluated in situ, using the transferase deoxyuridine end labeli ng (TUNEL) assay, and the expression profile of two apoptotic proteins, bcl -2 and bar. The proliferative index tvas determined on the basis of Ki-67 a ntigen immunoreactivity. RESULTS. Apoptosis in malignant prostate cells was significantly higher in African American than Caucasian men (11.6% vs. 4.2%, P < 0.001). Interestin gly, the rate of cell proliferation of prostate tumor cells was similar in the two ethnic groups (4.5% and 4.2%). The antiapoptotic protein bcl-2 was detected at significantly higher levels in tumors from Caucasian than Afric an-American patients (40.8% vs. 31.6%, P < 0.05). Expression of bar, the ap optosis promoter, was consistently high among tumor epithelial cells in spe cimens from both racial groups (68%). CONCLUSIONS. These findings provide a novel insight into the molecular dete rminants of tumor growth that may underlie the ethnic differences in prosta te cancer incidence and clinical behavior. Downregulation of bcl-2 expressi on may be potentially responsible for the loss of apoptotic control in pros tate tumors from African-American men. This study may have significant clin ical implications in the development of novel diagnostic approaches for bio logically aggressive prostate cancer from diverse racial origin. (C) 2000 W iley-Liss, Inc.