1455 Double Trouble: A Rare Case of Colonic Mixed Adenoneuroendocrine Carcinoma (MANEC)

Abstract

INTRODUCTION: Mixed adenoneuroendocrine carcinoma (MANEC) is a rare malignancy involving both epithelial and neuroendocrine components and accounts for fewer than 2% of all colorectal cancers. We present the case of a 34 yo male whose persistent weight loss and cramping abdominal pain led to the discovery of Stage IV MANEC. CASE DESCRIPTION/METHODS: 34 yo male with no significant past medical history presented with the chief complaint of diffuse abdominal cramps over the preceding 3 days. He had intermittent, non-bloody diarrhea, and endorsed 25-30 lb unintentional weight loss in the preceding 4 months. Labs were significant for a WBC of 17.3 U/L, CRP 94.4 mg/L, and sedimentation rate of 60 mm/hr. CT abdomen and pelvis was concerning for underlying inflammatory bowel disease. Before further work up, the patient left against medical advice. He returned 2 months later due to persistent symptoms. Gastrografin study and colonoscopy showed a circumferential, partially obstructing, ulcerated mass in the sigmoid colon (Figure 1). Biopsy of the lesion showed moderately differentiated adenocarcinoma. He underwent exploratory laparotomy, sigmoidectomy, and mesenteric lymph node dissection with pathology consistent for mixed adenoneuroendocine carcinoma with a high grade aggressive neuroendocrine component of the sigmoid with involvement of small bowel, bladder serosa, and lymph nodes (Figure 2). The metastatic component was exclusively high-grade neuroendocrine tumor. The patient subsequently underwent complete resection of primary and metastatic lesions and was started on Cisplatin and Etoposide for adjuvant chemotherapy. DISCUSSION: MANEC is a mixed tumor containing adenocarcinoma and neuroendocrine components each representing at least 30% of the tumor. It is hypothesized that the tumor arises from multi-potent endodermal progenitor cells with bi-directional differentiation into both epithelial and neuroendocrine neoplasms. Outcomes depend on each malignant component and the type of neuroendocrine cells present. Due to its neuroendocrine component, MANEC is more aggressive and advanced at the time of diagnosis with poorer outcomes as compared to adenocarcinoma. While no standardized treatment regimen has been identified for MANEC, currently accepted therapy involves complete resection of the primary and metastatic lesions with individually tailored adjuvant chemotherapy to help reduce its high recurrence rate.