The diagnosis of prostate carcinoma, especially when present in a limited amount in biopsy, is often challenging because numerous benign conditions have architectural and cytological features overlapping with and mimicking carcinoma. These mimics include various anatomic structures, inflammatory and reactive conditions, and pathophysiological conditions, including atrophy, hyperplasia, and metaplasia. Many of these lesions are readily recognized and separated from malignancy, but some may cause potential diagnostic difficulties.
A useful approach to classifying benign mimics is based on major growth patterns of prostate carcinoma outlined in the Gleason grading system. This approach provides a conceptual framework for considering differential diagnoses. Three major growth patterns are encountered: small well-formed gland pattern mimicking Gleason pattern 3 carcinomas; cribriform growth pattern mimicking Gleason pattern 4 carcinomas; and poorly formed/fused gland/nest/single cell pattern mimicking Gleason pattern 4 or 5 carcinomas. Most benign lesions mimic small gland (acinar) adenocarcinoma; however, mixture of growth patterns is also commonly encountered.
Before establishing a cancer diagnosis, pathologists should always consider and rule out various benign lesions that mimic carcinoma. Immunohistochemical markers should be utilized to support the morphological impression, and one should be aware about pitfalls and limitations of markers. This chapter outlines an overall approach, classification, description of pathologic features, and diagnostic pitfalls of each benign entity.
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