Primary small cell carcinoma of the stomach: a case report with an immunohistochemical and molecular genetic analysis.

Small cell carcinoma (SCC) of the stomach is extremely rare; about 110 cases have been reported in the world literature. Immunohistochemical studies of various antigens and genetic studies of KIT and platelet-derived growth factor-α (PDGFRA) have not been performed in gastric SCC. An 84-year-old man consulted our hospital because of epigastralgia and weakness. Blood test showed anemia and increased CA19-9 (233 U/ml). Endoscopic examination revealed a large Borrmann type III tumor measuring 6x8 cm in the stomach. Biopsies from the tumor revealed typical small cell carcinoma with very scant cytoplasm, hyperchromatic nuclei, absent nucleoli, molded nuclei, and increased nucleo-cytoplasmic ratio. Immunohistochemically, the tumor cells were positive for pancytokeratin (PCK) WSS, PCK MNF-116, PCK AE1/3, PCK CAM5.2, cytokeratin (CK) 34BE12, CK 5/6, CK7, CK8, CK18, vimentin, EMA, KIT (CD117), CD56, synaptophysin, chromogranin, NSE, CA19-9, CEA, p53 protein, and Ki67 antigen (Ki-67 labeling = 60%). The tumor cells were negative for CK14, CK19, CK20, PDGFRA, CD45, CD45RO, CD3, CD20, CD30, and CD79a. A retrospective genetic analysis using PCR-direct sequencing method in paraffin sections identified no mutations of KIT (exons 9, 11, 13 and 17) and PDGFRA (exons 12 and 18) genes. Various imaging modalities including CT and MRI showed multiple small metastases in the liver, bilateral lungs, and perigastric lymph nodes. The patient was thus inoperative. The patient is now treated by cisplatin-based chemotherapy four months after the first manifestation.