An Intramucosal Large Cell Neuroendocrine Carcinoma Arising Within a Tubulovillous Adenoma With High-Grade Dysplasia of the Rectosigmoid Colon Treated With Polypectomy

Abstract

High-grade neuroendocrine carcinoma (NEC) has been previously reported to arise within preexisting adenoma but is usually at an advanced stage and carries a dismal prognosis and is almost always treated with surgical resection. Intramucosal NECs treated with polypectomy have not been reported. Herein, we report the first case of intramucosal NEC treated by polypectomy. An 87-year-old white male was referred to the Cleveland Clinic for a polyp detected in an outside hospital. A 40 mm sessile polyp was visualized in the recto-sigmoid colon using flexible sigmoidoscopy. Polypectomy was performed and histopathology revealed multiple fragments of tubulovillous adenoma (TVA) with extensive high-grade dysplasia (HGD). Notably, there was a focus (1 mm) of NEC confined to lamina propria and intimately related to the adenomatous component. This focus of intramucosal NEC was confirmed by its strong and diffuse synaptophysin and chromogranin A immunoreactivity and near 100% Ki-67 labeling index. Immunohistochemistry using a panel of antibodies against mismatch repair proteins was performed and both the adenomatous and NEC components had normal staining for MLH1, PMS2, MSH2, and MSH6. This, to the best of our knowledge, is the first case of intramucosal NEC treated with polypectomy reported to date. Patient was alive 1 year after polypectomy. Clinical behavior remains to be seen with long-term follow-ups. J Med Cases. 2016;7(5):174-177 doi: http://dx.doi.org/10.14740/jmc1996w