Variants of acinar adenocarcinoma of the prostate mimicking benign conditions

Abstract

Histological variants of acinar adenocarcinoma of the prostate may be of significance due to difficulty in diagnosis or due to differences in prognosis compared to usual acinar adenocarcinoma. The 2016 World Health Organization classification of acinar adenocarcinoma includes four variants that are deceptively benign in histological appearance, such that a misdiagnosis of a benign condition may be made. These four variants are atrophic pattern adenocarcinoma, pseudohyperplastic adenocarcinoma, microcystic adenocarcinoma, and foamy gland adenocarcinoma. They differ from usual small acinar adenocarcinoma in architectural glandular structure and/or cytoplasmic and nuclear alterations. The variants are often admixed, in variable proportions, with usual small acinar adenocarcinoma that is often Gleason pattern 3 but may be high-grade pattern 4 in a minority of cases. Atrophic pattern adenocarcinoma can be identified in a sporadic setting or after radiation or hormonal therapy. This variant is characterized by cytoplasmic volume loss and can resemble benign glandular atrophy, an extremely common benign process in the prostate. The glands of pseudohyperplastic adenocarcinoma simulate usual epithelial hyperplasia, with gland complexity that is not typical of small acinar adenocarcinoma. These complex growth configurations include papillary infoldings, luminal undulations, and branching. Microcystic adenocarcinoma is characterized by cystic dilation of prostatic glands to a size that is much more commonly observed in cystic change in benign prostatic glands. Finally, the cells in foamy gland adenocarcinoma display cytoplasmic vacuolization and nuclear pyknosis, features that can found in benign glands and macrophages. Three of the four variants (atrophic, pseudohyperplastic, and microcystic) are assigned low-grade Gleason pattern 3. Of significance, foamy gland adenocarcinoma can be Gleason pattern 3 but can also be high-grade pattern 4 or 5. Diagnostic awareness of the existence of these deceptively benign-appearing variants of acinar adenocarcinoma is essential so that an accurate diagnosis of prostate cancer may be rendered.