Small cell neuroendocrine carcinoma of the prostate: incidence and a report of four cases with an examination of KIT and PDGFRA.

Because there have been no reports on the incidence and expressions and mutations of KIT and PDGFRA in small cell neuroendocrine carcinoma (SCNEC) of the prostate, the author surveyed archival specimens of 2,642 prostatic specimens (biopsy, 1,503 cases; transurethral resection, 1,009 cases; prostatectomy, 130 cases). Of these, 706 cases were malignant tumors. In equivocal cases (n = 16) of Gleason 5 adenocarcinoma resembling SCNEC, several neuroendocrine markers were immunohistochemically examined. As the results, four cases of SCNEC were identified; therefore the incidence of SCNEC was 0.5% of all prostatic malignancies. All the four cases were biopsies. The remaining 686 cases were adenocarcinomas. In case 1 (50 years of age), the SCNEC tumor cells were positive for cytokeratin, P504S, synaptophysin, KIT, and PDGFRA, but negative for PSA, neuron specific enolase, CD56, and TTF-1. In case 2 (70 years of age), the tumor cells were positive for cytokeratin, PSA, P504S, chromogranin, and synaptophysin, but negative for neuron-specific enolase, CD56, TTF-1, KIT, and PDGFRA. In case 3 (72 years of age), the SCNEC tumor cells were positive for cytokeratin, PSA, P504S, synaptophysin, CD56, KIT, and PDGFRA, but negative for neuron-specific enolase, chromogranin, and TTF-1. In case 4 (81 years of age), the SCNEC tumor cell were positive for cytokeratin, PSA, P504S, chromogranin, synaptophysin, neuron-specific enolase, KIT, and PDGFRA, but negative for CD56 and TTF-1. A molecular genetic analysis using PCR-direct sequencing showed no mutations of KIT (exons 9, 11, 13, and 17) and PDGFRA (exons 12 and 18) genes in three informative cases of SCNEC. The present cases were the first of prostatic SCNEC with an examination of KIT and PDGFRA expression and KIT and PDFGRA gene mutations.