Atypical acinar proliferations of the prostate

Small acinar lesions of the prostate may mimic prostate cancer. In the cent ral and transition zone of the prostate, atypical adenomatous hyperplasia ( AAH) must be differentiated from low grade carcinoma (Gleason score 2-5). I n the dorso-peripheral zone, high grade prostatic intraepithelial neoplasia (PIN) and atypical small acinar proliferations (ASAP) are the most importa nt lesions mimicking carcinoma. Further differentiation is necessary betwee n high grade PIN and intraductal carcinoma. ASAP, on the other hand, may mi mic low grade carcinoma. The significance of basal cell type cytokeratin im munohistochemistry (IHC) in the differentiation between ASAP and low grade carcinoma of the prostate was substantiated by additional MIB-1 IHC. The st atus of the basal cell layer in ASAP was found to be variable (complete, fr agmented and absent). Independent of the status of the basal cell layer, th e mean MIB-1 proliferation index of ASAP was significantly higher than that of clearly benign lesions and did not differ from that of low grade carcin oma. As carcinoma is frequently detected in rebiopsies, close clinical foll ow up of patients with ASAP is advisable.