S2075 Mixed Adeno-Neuroendocrine Carcinoma (MANEC) of Colon: Rare Differential Diagnosis for Iron Deficiency Anemia

Abstract

Introduction: Colonic Mixed adenoneuroendocrine carcinoma (MANEC) is a rare but highly aggressive tumor. In English Literature only 10 cases or less have been reported of this neoplasm, with the prognosis still unfavorable. Mixed adenoneuroendocrine carcinomas, by definition, are comprised of at least 30% of both a neuroendocrine and an adenocarcinomatous component. Cases are typically diagnosed at advanced stages, and the age of presentation is younger than the average age of colorectal adenocarcinoma (∼60 years old). Metastasis can occur anywhere but usually seen in the liver, regional lymph nodes and rarely peritoneum. The tumor neuroendocrine markers and immunophenotype are essential for the diagnosis, for example chromogranin, synaptophysin, CDX-2, and CD56. Case Description/Methods: A 53-year-old women with a history of abdominal pain was diagnosed with NET via histopathology of the cecum. The patient was referred to us by her hematologist which he ordered CT/pelvis due to her new onset of iron deficiency anemia and CT scan showed irregular bowel wall thickening of proximal ascending colon with infiltration and nodularity of surrounding fat suspicious of colon neoplasm. The patient has diabetes mellitus and hypertension other than that she had no significant history of past illness. A colonoscopy and biopsy were performed that showed poorly differentiated carcinoma with ulceration in large bowel mucosa, morphologically, high grade poorly differentiated malignant neoplasm was noted with ulceration. Histopathology and Immunohistochemical studies show the tumor cells are positive for AE1/3, CK7, synptophysin, CDX-2, while negative for CK20, chromogranin, CD56. Ki-67 shows a high labeling index (−95%). The negative stain of tumor cells for MLH-1 and PMS2 can be associated with microsatellite instability related germ line mutation. The differential diagnosis includes poorly differentiated adenocarcinoma, mixed adenoneuroendocrine carcinoma and large cell endocrine carcinoma. A definitive classification depends on the total resection specimen (Figure 1). Discussion: Mixed adenoneuroendocrine carcinoma of the colon is a neoplasm consisting of 2 components coexisting simultaneously within a tumor. It is a very rare carcinoma that presents at a younger age than colorectal adenocarcinoma. Unfortunately, it is diagnosed usually at late stages when metastasis has occurred. If detected at early stages curative surgery can be the treatment. The prognosis Is poor due to late diagnosis and dual nature of the tumor.Figure 1.: Histology and Immunohistochemical studies.