Paranuclear blue inclusions of small cell carcinoma of the stomach: report of a case with cytologic presentation in peritoneal washings

BACKGROUND: Primary gastric small cell carcinoma is a rare but important entity. We describe a case that we diagnosed by peritoneal washing cytology. CASE: A 70-year-old male presented with upper abdominal discomfort and underwent endoscopic evaluation. Gastric endoscopy revealed a diffuse, infiltrating tumor from the body to the antrum. Total gastrectomy with lymph node dissection and intraoperative peritoneal washing cytology were carried out. Peritoneal washing cytology showed the presence of many undifferentiated malignant small cells with a necrotic background. The tumor cells were small and round, with naked, hyperchromatic nuclei and finely granular chromatin. Some tumor cells contained paranuclear blue inclusions (PBls) in the cytoplasm. The tumor cells were positive for neuron-specific enolase and synaptophysin on immunocyto-chemistry. Carcinoembryonic antigen, alpha-fetoprotein (AFP) and leukocyte common antigen were negative. Pathologic diagnosis after the operation was moderately to poorly differentiated adenocarcinoma and small cell carcinoma containing AFP-positive cells. CONCLUSION: The prognosis of primary gastric small cell carcinoma is usually poor. Our patient died of multiple liver metastases and peritonitis carcinomatosa 69 days after surgery. When a gastric small cell carcinoma is suspected in peritoneal washings, immunocytochemical demonstration of neuroendocrine differentiation is required to arrive at the final diagnosis.