Mixed Adenoneuroendocrine Carcinoma: A Rare Tumor of the Gastrointestinal Tract

Abstract

Mixed adenoneuroendocrine carcinoma (MANEC) is a rare tumor of the gastrointestinal tract. Classification requires at least a 30% component of both an adenocarcinoma and a neuroendocrine carcinoma. There are only nine reported cases in the cecum, which makes this case exceptionally rare. A 55-year-old female presented with abdominal pain for one month. Physical exam was remarkable for mild abdominal distention and diffuse tenderness to palpation. Computed tomography (CT) abdomen/pelvis with contrast demonstrated a small bowel obstruction likely secondary to an inflammatory process in the terminal ileum. Gastroenterology performed a colonoscopy, which revealed a severe non-traversable stenosis in the terminal ileum. The patient was then started on high dose steroids due to concern for Crohn's ileitis. However, pathology was inconsistent with Crohn's. CT enterography revealed a six centimeter segment of ileum with irregular wall thickening and a nodular mucosal enhancement with a ten millimeter focus of enhancement concerning for a neoplastic process. Multiple adjacent mesenteric lymph nodes were also noted. An ileocolic resection was performed. Pathologic examination revealed a mixed adenoneuroendocrine carcinoma with invasion through the muscularis propria into the pericolonic adipose tissue and perineural invasion. Adenocarcinoma component was positive for CK20, CK7, and faintly positive CDX2. The neuroendocrine component was positive for CK7 synatophysin, and CD56 and negative for CK20 and CDX2. Ki67 showed a high proliferative rate (97%). All margins of resection were negative and patient was treated with folinic acid, fluorouracil, and oxaliplatin (FOLFOX). She completed two cycles with plan to continue chemotherapy outpatient. MANEC tumors have a high metastatic potential, which is attributed to the neuroendocrine component. Laboratory and imaging findings are inconsistent. Thus, diagnosis is based on the tumor architecture and must include immunohistochemisty. Tumors must stain positive for two of the following: chromogranin, synaptophysin, and/or CD56. Due to the rarity of the tumor, treatment is inconsistent and requires further future investigations.Figure: CT enterography showing a 6 cm segment of the ileum with irregular wall thickening and nodular mucosal enhancement with a 10 mm enhancing focus concerning for a neoplastic process.Figure: CT enterography showing a 10 mm enhancing focus in the ileum concerning for a neoplastic process.