Poorly Differentiated Neuroendocrine Carcinoma in a Perigastric Lymph Node from an Unknown Primary Site
A 52-year-old male patient was diagnosed as having early gastric cancer at the lesser curvature of the antrum by routine esophagogastroduodenoscopy in June 2008. He had no relevant previous medical history. Results of a subsequent endoscopic biopsy resulted in a histological diagnosis of well-differentiated adenocarcinoma. Computed tomography (CT) of the abdomen showed no evidence of LN enlargement or distant metastases. He was diagnosed as having type IIc early gastric cancer, which met the indications for endoscopic submucosal dissection (ESD). ESD was performed successfully (), and the resected specimen confirmed the presence of well differentiated adenocarcinoma, with negative resection margins, and the absence of lymphovascular or perineural invasion by hematoxylin and eosin (H&E) staining (). However, six months later, a LN enlargement measuring 2.0 cm at the lesser curvature side of the stomach was observed on a routine abdominal and pelvic CT scan (). He had no symptoms, and physical examination failed to reveal evidence of peripheral lymphadenopathy, and a meticulous skin examination revealed no suspicious lesions. He underwent subtotal gastrectomy and regional LN dissection under a suggestive preoperative diagnosis of gastric adenocarcinoma with perigastric LN metastasis. Microscopically, no residual tumor was found in the stomach, and the pathologic findings of the single perigastric LN differed completely from those of gastric adenocarcinoma. It was presented to PDNEC by morphology on H&E stain (). Results of immunohistochemical staining showed that tumor cells were positive for cytokeratin 20 (1 : 200, Leica, Newcastle-upon-Tyne, UK), CD56 (1 : 150, Leica) (), synaptophysin (1 : 200, NeoMarkers, Fremont, CA) (), and chromogranin (1 : 100, Leica) (), but negative for cytokeratin 7 (1 : 600, NeoMarkers), thyroid transcription factor-1 (1 : 300, Leica), S-100 (1 : 800, Dako, Glostrup, Demark), and human melanoma black 45 (1 : 150, Leica). Therefore, based on histological and immunohistochemical findings, a diagnosis of PDNEC was made. We performed immunohistochemistry in order to rule out neuroendocrine differentiation in previous well-differentiated adenocarcinoma from the ESD specimen; according to the results, all of the tumor cells were negative for CD56, synaptophysin, and chromogranin. In addition, when the ESD specimen and the specimen resected after subtotal gastrectomy were mapped, no other primary site was identified in the stomach specimen. In our search for the primary site, we also performed chest CT, bronchoscopy, colonoscopy, and a positron emission tomography-CT scan. After an extensive work up, no primary site was identified and no further metastatic lesions were found. He was diagnosed as having PDNEC of unknown origin in one perigastric LN. He also received four cycles of etoposide and cisplatin. He has remained disease-free for more than two years after surgical resection. Written informed consent was obtained from the patient for report of this case.