RESUMEN
An 86-year-old woman was admitted because of right lower abdominal pain. A 7 by 6 cm tumor palpable in the right lower quadrant was poorly mobile. Abdominal CT scan showed a huge tumor with a strong enhancement effect. Barium enema and colonoscopic examination revealed a submucosal tumor located from the cecum to the ascending colon on the oral side. An undifferentiated adenocarcinoma was suspected after examination of the biopsy specimen, right hemicolectomy was performed. The tumor invaded the retroperitoneal membrane. Histological examination showed a very atypical carcinoid tumor with central necrosis invading the veins. Pathohistologically, the huge tumor was diagnosed as endocrine cell carcinoma or atypical carcinoid. Furthermore, an elevated lesion, 2.5 cm in size, was revealed in the cecum closed to the huge tumor. Histological examination showed that the polypoid lesion was early moderately differentiated adenocarcinoma. There was no transition between the two tumors. The patient was discharged, but died of local recurrence 9 months after the surgery. Endocrine cell carcinoma of the large bowel is rare, in particular of the ileocecal region. Endocrine cell carcinoma of the ileocecal region adjacent to an adenocarcinoma without transition had not been reported previously in Japan.