S4701 Infiltrating Presacral Neuroendocrine Tumor: An Atypical Cause of Lower Gastrointestinal Bleeding

Introduction: Neuroendocrine tumors (NETs) are rare malignancies with an incidence of 8.19 per 100,000 people. Typical patterns demonstrate NETs tend to be asymptomatic until advanced stages and frequently identified within the gastrointestinal (GI) system. The presacrum is an exceedingly rare location for primary and metastatic NETs, that, when symptomatic, present with pelvic pain or fullness. We describe the case of an 82-year-old African American man with a metastatic presacral NET presenting with lower GI bleeding. Case Description/Methods: The patient had a history of a 10 mm, well-differentiated, G2 rectal NET with Ki67 index less than 5% located 8 cm from the anal verge, which was treated with complete endoscopic resection 15 years prior to presentation. There was 1 recurrence of local disease, also treated with complete endoscopic resection 10 years prior. Metastases to bone and liver were identified on imaging 4 years prior, and the presacrum 2 years prior. The metastatic disease was treated with systemic chemotherapy, but this was stopped 4 months prior to current presentation. On admission, hemoglobin was 11.0 g/dL which decreased to 6.4 g/dL the following day. He was given 3 units of packed red blood cells. Colonoscopy identified a large clot adherent to pale, dusky, necrotic appearing rectal mucosa. There were 3 fistulous tracts identified. The mucosa proximal to 8 cm from the anal verge appeared normal. Computed tomography angiography of the abdomen and pelvis demonstrated a large presacral, contrast-enhancing tumor filling the majority of the pelvis with cystic and necrotic changes. The tumor was contiguous with the rectum, without differentiation between the structures and with connecting fistulous tracts. There was no evidence of mass within the rectum on colonoscopy or imaging. Discussion: The prognosis of NETs can be difficult to predict. The majority of rectal NETs are less than 1 cm and do not invade deeper than the submucosa, making them amenable to endoscopic resection. The risk of metastatic disease is low at 5% for lesions less than 1 cm. In this case, the patient had complete endoscopic resection with negative margins, but intermediate grading based on Ki67 index. On review of the literature, we have not identified any reported cases of metastatic presacral lesions eroding into the rectum or presenting with lower GI bleeding. Interestingly, it appears that the location of erosion from the presacral tumor is he same location as the index tumor. This case highlights a rare presentation of a rare disease.