[Suspicious acinar proliferations of the prostate]

A variety of small acinar lesions of the prostate may mimick prostate cancer. In the central and transition zone of the prostate atypical adenomatous hyperplasia (AAH) has to be differentiated from low grade carcinoma (Gleason score 2-6). In the dorso-peripheral zone high grade PIN (prostatic intraepithelial neoplasie) and ASAP (atypical small acinar proliferations) represent the most important mimicers of carcinoma. High grade PIN has to be differentiated from intraductal carcinoma, ASAP on the other hand may mimic low grade carcinoma. The significance of basal cell type cytokeratin immunhistochemistry (IHC) in the differentiation between ASAP and low grade carcinoma of the prostate is assessed by additional MIB-1 IHC. The status of the basal cell layer in ASAP was shown to be variable (complete, fragmented and partial loss). Independently from the status of the basal cell layer the mean MIB-1 proliferation index of ASAP was significantly higher than of clearly benign lesions and did not differ from that of low grade carcinoma. Taking into account the high detection rate of carcinoma in repeat biopsies, close clinical follow up of patients with ASAP should be recommended.