ABSTRACT
Atypical epithelial proliferations of the prostate resembling carcinoma have been known for more than 50 years. Atypical small acinar hyperplasia closely resembles small acinar carcinoma of the prostate. The accurate differential diagnosis is of great importance. Atypical small acinar hyperplasia is defined as a focal non-neoplastic proliferation of small acini lined by a single layer of epithelial cells with clear cytoplasm. Atypical hyperplasia grows in an organoid fashion; connection to a parent duct often can be identified. The nuclei of the benign small acini are quite similar to the nuclei of the epithelial cells lining the nearby normal ducts. The nuclei in microacinar carcinoma are generally different from the nuclei noted in the benign ducts. The glandular patterns markedly vary within a circumscript area of atypical hyperplasia. Nonrigid, collapsible gland structure characterizes the individual acini in atypical hyperplasia. The malignant acini in well-differentiated prostatic carcinoma are rigid, unyielding.
