Synchronous large-cell neuroendocrine carcinoma and adenocarcinoma of the colon.

Large-cell neuroendocrine carcinoma of the colon is a rare entity with a prognosis that is usually poor due to the high likelihood of early metastasis. A 61-year-old man had surgery for colon cancer of the transverse colon and cecum. Microscopic examination of the tumor showed that the location was the proximal transverse colon, with small nests containing rosettes and palisading patterns of large tumor cells with faintly granular cytoplasm. The immunohistochemistry was positive for synaptophysin and chromogranins. The tumors were diagnosed as a large-cell neuroendocrine carcinoma of the colon. In addition, the tumor of the cecum showed microscopic findings consistent with a well-differentiated adenocarcinoma. The immunohistochemical panel showed that the tumor was negative for neuroendocrine markers. There were no clinical findings suggestive of hormone hypersecretion. Cancer metastasis was found in the peritoneum section of the small bowel. Postoperative chemotherapy was applied. The patient was alive with good performance after, and there was no sign of tumor progression. This is the first case of a synchronous large-cell neuroendocrine carcinoma and adenocarcinoma of the colon. The patient was treated successfully with debulking surgery and systemic chemotherapy.