Abstract
Mixed adenoneuroendocrine carcinoma (MANEC) is an extremely rare tumor of the GI tract that consists of a dual adenocarcinomatous and neuroendocrine differentiations, with each component representing at least 30% of the tumor. In this case, we report a 58-year-old male diagnosed with MANEC in the descending colon. A 58-year-old male with a past medical history of CVA, hypertension, and diabetes was evaluated for chronic blood loss anemia requiring transfusions. He underwent a colonoscopy which demonstrated two polyps in the descending colon. Pathology of the larger polyp revealed infiltrating carcinoma arising in the background of a tubular adenoma. Solid nests of neoplastic neuroendocrine cells could be seen invading into the submucosa through the muscularis mucosae. Immunoperoxidase stains demonstrated positivity for CDX2 and synaptophysin, with patchy positive staining with CD56. Stains were negative for CK7, CK20, chromogranin A, and neuron-specific enolase (NSE). Based on the above histopathological findings, a diagnosis of MANEC was made. A MANEC in the cecum was first described by Cardier in 1924. Since then only few cases were reported. MANEC is an aggressive tumor due to the neuroendocrine portion of the neoplasm. Diagnosis is mainly based on the tumor architecture, along with immunohistochemical staining using neuroendocrine specific markers such as chromogranin, synaptophysin, CD56, and NSE. MANEC tends to metastasize rapidly. The management of MANEC is not clear due to the unexplained behavior of this tumor. Much like other malignancies, early surgical resection may be curative. Patients with MANEC lesions containing a higher ratio of the adenocarcinoma component may have a better prognosis than patients with a lower ratio. In general, patients with GI MANEC tend to have a poor prognosis, with a median survival of 7-10 months after the initial diagnosis. In conclusion, we are reporting a case of MANEC in the colon to increase physician awareness of MANEC, its diagnosis, optimal treatment, and prognosis.