Paneth cell-like change of the prostate gland. A histological, immunohistochemical, and electron microscopic study.

Paneth cell-like change (PCLC) of the prostatic glandular epithelium was focally observed in one case of normal glandular epithelium, two cases of glandular and stromal hyperplasia, one case of prostatic intraepithelial neoplasia, and four cases of prostatic adenocarcinoma. The distinctive cells were characterized by bright, eosinophilic cytoplasmic granules on routine hematoxylin and eosin-stained material. The cytoplasmic granules in the benign prostatic epithelium were periodate-Schiff's procedure (PAS)-positive and diastase resistant and immunohistochemically negative for lysozyme, neuron-specific enolase, chromogranin, and serotonin. The eosinophilic granules in the prostatic intraepithelial neoplasia and adenocarcinoma cases were immunohistochemically positive for chromogranin, serotonin, and neuron-specific enolase, and negative for lysozyme. By electron microscopy the eosinophilic granules represented exocrine-like or lysosomal-like vesicles in the benign epithelium and neuro-endocrine granules in the malignant epithelium. The lesion represents a prostatic epithelial PCLC rather than a Paneth cell metaplasia. PCLC is the common histological manifestation of two different phenomena: (a) a PAS-positive and diastase-resistant eosinophilic cytoplasmic granular change in benign prostatic epithelium, and (b) endocrine differentiation with neuroendocrine granules in dysplastic and malignant prostatic epithelia. The importance of recognizing PCLC lies in its differentiation from other possible prostatic cytoplasmic inclusions.