S3675 Unusual Presentation of Neuroendocrine Tumor in Rectum

Introduction: Neuroendocrine tumors are epithelial, heterogeneous neoplasms, ranging from indolent, well-differentiated tumors to very aggressive, poorly differentiated neuroendocrine carcinomas. The rectum is the second most frequent site, representing 1-2%. Most are asymptomatic and detected incidentally. Up to 90% of lesions are less than 10 mm in size, confined to the submucosa and well differentiated, so endoscopic resection is an option. Case Description/Methods: 70-year-old woman, with a history of controlled arterial hypertension, started with symptoms of dyspepsia accompanied by changes in the defecatory habit of 3 months of evolution. The fecal occult blood test was positive. Colonoscopy was scheduled, showing an elevated lesion of polypoid appearance 6 centimeters from the anal margin, with a superficial mucosa of normal appearance, mobile, approximately 1 cm, on inspection of the mucosa with NBI without alteration. Polypectomy was successful Histology showed malignant neoplasm formed by monotonous cells of small size, well defined borders, with eosinophilic cytoplasm, round or oval nuclei with clumped chromatin, giving it a salt and pepper appearance within the nucleus. The immunohistochemical study was positive for chromogranin and ki67. A diagnosis of well-differentiated neuroendocrine tumor, WHO grade 1, was made. Discussion: Rectal neuroendocrine tumors are observed as small round polypoid lesions, characterized by a smooth mucosa of normal appearance, the atypical findings are semi-pedunculated appearance, hyperemia, central depression, erosion and ulceration. They are found between 4 and 10 cm above the dentate line, on the front or lateral wall of the middle rectum, located in the submucosa, without invading the muscularis propria. The risk of metastasis ranges between 3-60%, therefore, early detection and elimination is important. The diagnosis was established by histology and immunohistochemistry results and classified according to the proliferation index (mitotic count and Ki67-related proliferation index). Treatment will depend on whether it is localized, locally advanced or advanced metastatic disease.