eP678 - A Rare Case of Presacral Neuroendocrine Tumor Treated with Combined Robotic Dissection and Kraske Procedure

Purpose/Background: The boundaries of the presacral space are the rectum anteriorly, the sacrum posteriorly, and the endopelvic fascia laterally. Most of the tumors of this space are benign, and rarely seen, however several reports of malignant tumors, including neuroendocrine neoplasms (NEN) have also been found. Any part of the body can be the primary site of origin for NENs, but about 60% of cases originate in the gastrointestinal tract and about 30% originate in the bronchopulmonary tract. The presacral NENs usually behave as well-differentiated tumors with local involvement in the presacral area, but cases with distant metastases have also been reported. Immunohistochemistry can be used to attempt to identify the primary source of origin. To the best of our knowledge, about 70 cases have been reported so far, mainly in single case reports or small series. Given the rarity of this disease, data on treatment outcome is lacking. We present a case on a presacral NEN.Methods/Interventions: The patient is a 63 years old male who noticed a right sided buttock mass with occasional discomfort when sitting. He denied erythema, drainage, change in bowel habits or bladder function. A colonoscopy 7 years before was normal. The mass was evaluated with US, CT scan and later magnetic resonance imaging (MRI) confirming the presence of the cyst, with dimensions of 13.7 x 9.4 x 8.3 cm, unilocular in the presacral soft tissues, extending into the right medial gluteal subcutaneous fat. No septation or nodular internal enhancement were seen to suggest malignant degeneration. No infiltration of adjacent structures(Fig.1). He was treated operatively with a combined robotically assisted laparoscopic excision of retrorectal cyst with posterior rectum mobilization and Kraske procedure.Results/Outcomes: The patient had an unremarkable brief stay in the hospital. The histopathological of the specimen resulted back as low grade NEN with clear margins, Ki-67 < 1% with low chromogranin A (93 ng/mL) and normal 5-HIAA (2 mg/gCR) levels. PET scan without avid tracer for malignancy. Nine months after his surgery, a lesion in the pancreatic head and uncinate process, suspicious for adenocarcinoma on MRI, was confirmed with fine needle aspiration. He underwent neoadjuvant chemotherapy and Whipple procedure. The pancreatic specimen obtained did not demonstrate cancer. No recurrence of his disease has been seen.Conclusion/

Discussion: Given the benign findings on the pre-operative imaging and the rare incidence of presacral NEN, the patient had his final diagnosis obtained with the surgical specimen. Most cases of presacral NENs have been published as single case reports or small series. The majority of cases have been treated with local resection, as in this case, and information is scarce regarding follow-up, metastasis, and systemic treatment8. When systemic therapy is necessary, somatostatin analogs have been used as effective treatment for presacral NEN. The majority of tumors are non-functioning and somatostatin receptor positive. Extrapolating what is known for the other areas of gastrointestinal tract NEN, peptide receptor radionuclide therapy and tyrosine kinase have been tried with the former demonstrating promising activity and the latter warranting further investigations. Further prospective evaluation of this rare tumor entity is needed.Presacral Mass MRIFig.1 - MRI presacral mass