Objective: The aim of this study was to review the histological features and to define parameters distinguishing atypical adenomatous hyperplasia from prostatic adenocarcinoma grade 1 and 2. We evaluated 14 parameters related with cytological properties.

Material and Method: We found 11 atypical adenomatous hyperplasia (22 foci) and 15 prostatic adenocarcinoma grade 1 and 2 (22 foci) lesions in 105 radical prostatectomy specimens. Basal cell-specific keratin (34βE12) was applied and based on the fact that prostatic adenocarcinoma grade 1 and 2 lesions do not have basal cells we grouped the lesions as atypical adenomatous hyperplasia and prostatic adenocarcinoma grade 1 and 2.

Results: Statistically significant differences were found between atypical adenomatous hyperplasia and prostatic adenocarcinoma grade 1 and 2 lesions for some parameters including the largest nuclear diameter, nuclear location, 1-2 μm nucleolus, > 2 μm nucleolus, and nuclei containing multiple nucleoli. We found similar properties between the two lesions for the following parameters: irregularity of nuclear membrane, median diameter of the nucleolus, chromatin pattern, pynotic nucleus, nuclear pleomorphism, < 1 μm nucleolus nucleolar margination, and the ratio of nucleus to cytoplasm and the appearance of cytoplasm in the secretory cells.

Conclusion: Evaluation of the overall histomorphological criteria is important in the differentiation of atypical adenomatous hyperplasia and prostatic adenocarcinoma grade 1 and 2 lesions.