Options and Considerations in the Management of Peritoneal Disease in Patients with Small Bowel Neuroendocrine Tumors.

Opinion statement: Peritoneal metastases (PM) in small bowel neuroendocrine tumors (SBNET) are challenging. These patients have worse oncologic outcomes and may have symptoms related to mechanical obstruction and hormone production. Difficult decisions apply in diagnosis, surgical selection, postoperative systemic therapy, and surveillance. To aid in these decisions, we routinely recommend obtaining somatostatin receptor based functional imaging (i.e. DOTA PET/CT) and arterial and venous phase CT preoperatively to evaluate disease burden and guide surgical planning. Disease biology should also guide surgical management. The presence of synchronous liver metastases should not exclude patients from surgery. For patients with PM and grade 1 or 2 well differentiated SBNETs, we recommend aggressive surgical cytoreduction with the goal of a completeness of cytoreduction (CC) of 0 or 1 and > 70% cytoreduction of liver metastases. For high grade (G3) well differentiated SBNETs, surgical intervention may still be considered. In patients where the extent of disease does not allow for effective cytoreduction, or where patient comorbidities preclude extensive surgery, palliative surgeries or interventions may be preferred. Postoperatively, radiologic surveillance is important to evaluate for disease progression. Some SBNET patients presenting without PM are at risk of developing PM in follow-up, especially those with liver metastases or high T stage. In patients with progression or inoperable disease, systemic therapy including somatostatin analogs (SSAs), chemotherapy or peptide receptor radionuclide therapy (PRRT) may be potential options, although the latter may pose increased risk of bowel obstruction. When cytoreducton and systemic therapy are no longer options, palliative measures should be employed. Because of this complexity, management of PM in SBNET patients is a multidisciplinary collaborative effort.