An Extremely Rare Presentation of Large Cell Neuroendocrine Carcinoma of the Transverse Colon

Introduction: Large cell neuroendocrine carcinoma (LCNEC) is a rare and deadly cancer with a poor prognosis. The majority of cases affect the lungs and gastrointestinal tract, but it can affect any part of the body. Colon and rectal neuroendocrine carcinomas are rare, accounting for less than 1% of all colon and rectal cancers. We present the unusual case of an 85-year-old woman with large cell neuroendocrine carcinoma of the transverse colon. Case Description/Methods: An 85-year-old woman with a significant PMH of CKD and anemia of chronic disease presented to the hospital with abnormal labwork.The patient reported vague abdominal symptoms but denied having any hematochezia, melena, or hematemesis. She reported a prior colonoscopy in 2015 without any definitive pathology. Her physical exam was benign. Labs revealed significant iron deficiency anemia but she refused a transfusion of blood product. CT scan showed approximately 5 cm of thickening involving the transverse colon with an adjacently mildly enlarged mesenteric lymph node and a hypodense lesion seen in the inferior right hepatic lobe suspicious for metastasis. During colonoscopy the mass was biopsied but there were further complications by a localized perforated rectum during retroflexion. She required a diverting loop ileostomy and was ultimately discharged home with no significant complaints. Pathology revealed large cell neuroendocrine carcinoma with extramural venous invasion and infiltration of the mucosa propria into pericolic tissue. Tumor markers showed a high mitotic rate and immunochemistry stains were noted to be positive for Ki-67, PAN CK, CDX2, synaptophysin, and chromogranin. Furthermore, the pathology also indicated 9 of the 13 lymph nodes were positive for metastatic carcinoma. Patient was later followed by oncology but due to the patient's age and medical comorbidities, chemotherapy was not pursued (Figure). Discussion: An Extremely Rare Presentation of Large Cell Neuroendocrine Carcinoma of the Transverse Colon Neuroendocrine tumors are rare neoplasms that present with a variety of clinical presentations. A large neuroendocrine tumor is a subtype of neuroendocrine tumors that are aggressive in nature, often present with metastasis, and a poor prognosis. Colonic NETS are exceptionally rare accounting for only 0.2% of all colorectal cancers. Prognosis is relatively poor with a median survival of 10.4 months. Our case highlights a rare case presentation of a large neuroendocrine tumor.Figure 1.: Gross imaging and histopathology showing evidence of large neuroendocrine tumor.