[Collision Tumor Consisting of Sigmoid Colon Adenocarcinoma and Dissemination of Gastric Adenocarcinoma].

A 76-year-old man with sigmoid colon cancer and gastric cancer was referred to our hospital because of severe anemia. Computed tomography revealed peritoneal dissemination and lung metastasis. For diagnoses of cStage Ⅳa sigmoid cancer and cStage ⅣB gastric cancer, palliative laparoscopic sigmoidectomy and distal gastrectomy were planned in order to avoid tumor hemorrhage and intestinal obstruction. Intraoperative findings suggested cancer dissemination on the pelvic peritoneum, thus laparoscopic Hartmann's procedure and distal gastrectomy were performed. The final diagnosis was sigmoid colon cancers, ①pT4, ②pT2N2aM1c2(P2, PUL1), pStage Ⅳc and gastric cancer, pT4aN1M1(PER), pStage Ⅳ. The resected specimen showed collision tumors consisting of sigmoid colon cancer(CK20+/CK7-)and dissemination of gastric cancer (CK20-/CK7+)confirmed by immunohistochemistry. Postoperatively, the patient underwent chemotherapy for gastric cancer. We report here a rare case of collision tumor consisting of a sigmoid colon adenocarcinoma and peritoneal dissemination of gastric adenocarcinoma.