Paneth cell-like change and small cell carcinoma of the prostate. Two divergent forms of prostatic neuroendocrine differentiation.

Paneth cell-like change of the prostate refers to collections of prostatic cells with eosinophilic cytoplasmic granules that bear a striking histological resemblance to normal intestinal Paneth cells. Paneth cell-like change in malignant prostatic epithelium usually represent neuroendocrine differentiation, with neuroendocrine granules confirmed by immunohistochemical and ultrastructural studies. We report the histopathological, immunohistochemical, and electron microscopic findings in a mixed adenocarcinoma with Paneth cell-like change and small cell undifferentiated carcinoma. This case illustrates two divergent forms of neuroendocrine differentiation occurring in a single prostatic neoplasm. The spectrum of neuroendocrine differentiation in the prostate should be expanded to include tumors with Paneth cell-like change in addition to carcinoid tumors and small cell undifferentiated carcinoma. These three distinct forms of prostatic neuroendocrine neoplasia appear to correlate with three size ranges of neuroendocrine granules seen by electron microscopy.