Abstract
A challenge in the diagnosis of prostate pathology is the numerous benign mimics of prostatic adenocarcinoma. Most of these lesions have no clinical significance but may be misinterpreted as cancer in biopsy specimens. In this review we describe the features of some of the more common benign mimics and discuss how they can be distinguished from carcinoma. The diagnostic entities most commonly associated with a false positive diagnosis of cancer are the atrophic group of lesions that include simple atrophy, partial atrophy and post-atrophic hyperplasia. Benign proliferations exhibit architectural atypia, often with closely packed small glands, but with no or little nuclear atypia. The most common diagnostic pitfall of this group is adenosis, which may have an even more atypical architecture than some cancers. A common denominator of atrophy and benign proliferations is that they consist of small glands that may have a patchy or absent basal cell layer, which adds to the diagnostic difficulties. Amongst hyperplastic and metaplastic lesions, basal cell hyperplasia may be misinterpreted as cancer because of its dark basophilic glands that sometimes display a certain degree of nuclear atypia and occasionally exhibit a pseudoinfiltrative pattern. The most important extraprostatic anatomical structure causing diagnostic difficulties is the seminal vesicle. The closely clustered small glands and often strikingly atypical nuclei of seminal vesicle epithelium may be misinterpreted as cancer. Awareness of these mimics is of paramount importance for the practicing pathologist as a false positive diagnosis of prostate cancer may lead to unnecessary radical therapy.