Synchronous Colonic Neuroendocrine Tumor and Adenocarcinoma: A Case Report with Literature Review

Abstract

Multiple primary malignancies are categorized as synchronous and metachronous tumors, depending on the different rules of international institutions. The synchronous occurrence of a colonic neuroendocrine tumor with adenocarcinoma is rare. We present a case involving a synchronous colonic neuroendocrine tumor and adenocarcinoma. Our patient is a 68-year-old male with a positive stool occult blood test from a check-up examination. A biopsy of an unknown location from a colonoscopy revealed a moderately differentiated adenocarcinoma. His whole-abdominal computed tomography (CT) scan showed focal eccentric thickening with solid enhancement of the hepatic flexure colon. The patient underwent a right hemicolectomy. Macroscopic examination revealed an ulceroproliferative mass at the hepatic flexure and a submucosal mass at the cecum. The mass at the hepatic flexure exhibited villous, back-to-back, and cribriform glands composed of columnar cells with some tumor cells floating in extracellular mucin that were positive for CK20 and CDX2 immunostaining, diagnosed as a well-differentiated adenocarcinoma with mucinous features. The mass at the cecum revealed nest, trabecular, and glandular patterns of monotonous cuboidal to polygonal cells that tested positive for synaptophysin, chromogranin A, and CDX2 immunostaining, diagnosed as a well-differentiated neuroendocrine tumor. Many hypotheses have been proposed regarding the pathogenesis of neuroendocrine neoplasms with other primary malignancies. In our opinion, a genetic abnormality of common cell origin might be one of the possible etiologies of our case due to the common endodermal origin and the positivity of CDX2. We recommend that close surveillance for synchronous tumors in patients with colorectal neuroendocrine tumors might be helpful.