Benign mimickers of prostatic adenocarcinoma.

The diagnosis of prostatic adenocarcinoma, especially when present in small amounts, is often challenging. Before making a diagnosis of carcinoma, it is prudent for the pathologist to consider the various benign patterns and processes that can simulate prostatic adenocarcinoma. A useful method of classifying benign mimickers is in relationship to the major growth patterns depicted in the classical Gleason diagram. The four major patterns are small gland, large gland, fused gland and solid. Most mimickers fit within the small gland category and the most common ones giving rise to false-positive cancer diagnosis are atrophy, post-atrophic hyperplasia, atypical adenomatous hyperplasia and seminal vesicle-type tissue. A number of other histoanatomic structures such as Cowper's gland, verumontanum mucosal glands, mesonephric glands and paraganglionic tissue may be confused with adenocarcinoma. Additionally, metaplastic and hyperplastic processes within the prostate may be confused with adenocarcinoma. Furthermore, inflammatory processes including granulomatous prostatitis, xanthogranulomatous prostatitis and malakoplakia may simulate high-grade adenocarcinoma. Atypical adenomatous hyperplasia (adenosis), a putative precursor of transition zone adenocarcinoma, has overlapping features with low-grade adenocarcinoma and may cause problems in differential diagnosis, especially in the needle biopsy setting. The pathologist's awareness of the vast array of benign mimickers is important in the systematic approach to the diagnosis of prostatic adenocarcinoma. Knowledge of these patterns on routine microscopy coupled with the prudent use of immunohistochemistry will lead to a correct diagnosis and avert a false-positive cancer interpretation.