P1-10-5MIXED CANCER OF SMALL CELL CANCER AND ADENOCARCINOMA IN THE STOMACH

Abstract Small cell cancer of the stomach is rare, accounting for 0.06 to 0.95% of all gastric cancers with no established treatment although it grows fast and has poor prognosis. In this study, we experienced a mixed case of well-differentiated adenocarcinoma and Thyroid transcription factor-1 (hereinafter, referred to as TTF-1)–positive small cell carcinoma. A 75-year old man seen for abdominal bloating was found in upper gastrointestinal endoscopy to have a Borrmann 0-IIa + IIc type lesion of approximately 1 cm at the lesser curvature of the gastric antrum. Biopsy yielded a diagnosis of well-differentiated adenocarcinoma. Endoscopic submucosal dissection was performed and gastric cancer comprising both well-differentiated adenocarcinoma within the mucous membrane and small cell carcinoma invading to the submucosa accompanying lymphatic and blood vessel invasion was found. According to immunostaining, the small cell carcinoma was Chromogranin A-positive, Synaptophysin-positive, and diffusibly TTF-1-positive; however, no apparent tumor lesions were observed in other organs including the lung, there were no findings indicating any distant metastasis of the gastric cancer, and so distal gastrectomy and lymph node dissection were carried out. There was no remaining cancer in the resected specimen and lymph node metastasis was not observed. Postoperative prognosis is good and the patient is followed up without undergoing adjuvant chemotherapy; he is currently alive without relapse 5 months following gastrectomy. There is a report that the TTF-1-positive rate in lung adenocarcinoma was higher in well-differentiated tumors than undifferentiated tumors. TTF-1-positive small cell cancer of the stomach is very rare; the TTF-1-positive rate may contribute to the prediction of prognosis and treatment selection, and so we believe that accumulation of cases is very important.