Preoperative Diagnostic Dilemma in Rapidly Progressive Mixed Neuroendocrine-Nonendocrine Neoplasm of the Ascending Colon: A Case Report

Introduction:Mixed neuroendocrine-nonendocrine neoplasms (MiNENs) of the digestive tract are rare. They contain both neuroendocrine and nonendocrine components. We here report a rare case of a metastatic MiNEN originating in the ascending colon. Case Presentation:An 80-year-old man presented with abdominal pain and vomiting. Colonoscopy showed an obstructing mass in the ascending colon, and a biopsy resulted in diagnosis of an adenocarcinoma. A CT scan revealed multiple liver metastases. Thus, our diagnosis was stage IV colon adenocarcinoma (cT4aN1bM1a according to TNM Classification of Malignant Tumors). The primary lesion was resected to alleviate symptoms. Histopathological and immunohistochemical examination revealed a well-differentiated adenocarcinoma and a small-cell neuroendocrine carcinoma, leading to the diagnosis of a MiNEN. The patient declined postoperative treatment and died approximately 2 months after the surgery. Conclusion:The incidence of MiNENs may be underestimated because they lack typical symptoms or imaging features and are therefore often only diagnosed after resection. Awareness of colonic MiNENs and further accumulation of cases are necessary to improve the outcomes.