Primary small cell carcinoma of prostate without immunoreactive neuroendocrine proteins but with expressions of KIT and platelet‐derived growth factor‐α

Primary small cell carcinoma of the prostate is extremely rare. Herein reported is a case of primary small cell carcinoma of the prostate with immunohistochemical examination of KIT and platelet‐derived growth factor‐α. The present case is unique in that the small cell carcinoma did not express neuroendocrine antigens. A 68‐year‐old man was found to have high serum prostate‐specific antigen, and biopsy showed malignant small tumor cells fulfilling the small cell carcinoma criteria of the World Health Organization. Immunohistochemically, tumor cells were positive for pan‐cytokeratin, KIT, platelet‐derived growth factor‐α, p53, Ki‐67 labeling = 65%, prostate‐specific antigen and alpha‐methylacyl‐CoA racemase. Tumor cells were negative for vimentin, CD56, synaptophysin, chromogranin and neuron‐specific enolase. Imaging modalities showed multiple metastases, and the patient was treated by chemotherapy. The present report is the fifth with immunohistochemistry of prostatic small cell carcinoma.