Zonal origin of prostatic adenocarcinoma: are there biologic differences between transition zone and peripheral zone adenocarcinomas of the prostate gland?

Prostatic adenocarcinomas predominantly arise in the peripheral zone (PZ) of the organ; however, a significant subset of tumors (approximately 20%) originate in the transition zone (TZ). These tumors exhibit morphologic and growth pattern features suggestive of a lower degree of biologic aggressiveness. From our surgical pathology files, we identified 39 consecutive radical prostatectomy specimens in which discrete adenocarcinomas of both peripheral and transition zone origin were present. All specimens had been entirely embedded, step-sectioned, and reviewed by two urologic pathologists. DNA content was determined by image analysis of Feulgen-stained tissue sections, and cellular proliferation was evaluated by immunohistochemical staining with MIB-1. The mean Gleason score for the PZ and TZ tumors was 6.7 and 5.6, respectively (p < 0.001). Of 15 cases analyzed to date, 8 PZ tumors and 2 TZ tumors were aneuploid (p = 0.055). The proliferation indices for the PZ and TZ tumors were 5.0% and 1.6%, respectively (p < 0.05). These findings confirm other reports, supporting the concept of biological differences between carcinomas of peripheral and transitional zone origin.