S1780 An Unexpected Outcome of Incidental Rectal Nodule

Abstract

INTRODUCTION: Well differentiated neuroendocrine tumors (NETs) most commonly originate in the gastrointestinal (GI) tract. Generally speaking, NETs are relatively rare tumors, with an age-adjusted incidence for non-pancreatic primaries of 4.7 per 100,000. Within the GI tract, the most common site for NETs is the small intestine, followed by rectum, appendix colon, and stomach. CASE DESCRIPTION/METHODS: We present a case of a 39-year-old female with no significant past medical history referred by an outside gastroenterologist for endoscopic ultrasound (EUS) and possible resection of rectal subepithelial lesion (SEL) identified on colonoscopy performed for evaluation of diarrhea. On EUS the SEL was found to be well-circumscribed, hypoechoic, homogeneous, arising from muscularis mucosa and measuring approximately 3 × 5 mm (Figure 1a). The SEL was then removed by band-assisted endoscopic mucosal resection (EMR) utilizing Boston Scientific Captivator EMR device (Figure 1b). Pathologic review revealed that the SEL was a well-differentiated NET (Figure 2a) with immunohistochemical staining positive for synaptophysin (Figure 2b) and negative for chromogranin. Ki-67 was positive in <1% of tumor cells (Figure 2c). The findings were compatible with a carcinoid tumor and the resection margins were noted to be negative. The patient subsequently underwent a dotatate PET-CT scan that showed dotatate avid implants within the pelvis as well as small dotatate avid retroperitoneal lymph nodes consistent with metastatic carcinoid (Figure 3). Currently she remains asymptomatic and under observation by oncology without administration of systemic therapy. DISCUSSION: Rectal NETs are usually asymptomatic and found incidentally on endoscopy that is being performed for another reason. Most rectal NETs are localized at the time of diagnosis, however, the size of the tumor correlates with the likelihood of metastatic disease. Tumors that are smaller than 1.0 cm are infrequently metastatic. Approximately 6 percent of tumors between 1 and 1.9 cm are metastatic and 24 percent of those over 2 cm metastasize to the liver. Other features that portend a poor prognosis include deep invasion into the muscularis propria or deeper, lymphovascular invasion and high mitotic rate (≥2 per 50 high-power fields). Treatment for neuroendocrine tumors range from observation in asymptomatic patients to surgical resection to systemic therapy with somatostatin analogs. The treatment of choice is tailored to each individual patient.Figure 1.: (a) EUS image of subepithelial rectal lesion; (b) endoscopy image showing band application prior to endoscopic mucosal resection (EMR).Figure 2.: (a) Pathology slide displaying medium magnification of rectal neuroendocrine tumor; (b) Pathology slide of rectal neuroendocrine tumor with synaptophysin stain; (c ) Pathology slide of rectal neuroendocrine tumor with Ki-67 stain.Figure 3.: Imaging displaying dotatate avid implants in pelvis.