The meaning of R1 resection after endoscopic removal of gastric, duodenal and rectal neuroendocrine tumors

IntroductionWell-differentiated gastric, duodenal, and rectal neuroendocrine neoplasms (NETs) are rare diseases usually managed by endoscopic treatment. Although several endoscopic techniques are available, the number of patients with incomplete (R1) resection is significant.Areas coveredThis review focuses on the meaning of incomplete R1 findings after endoscopic resection in type I gastric NETs; nonfunctioning, non-ampullary duodenal NETs; and small rectal NETs. Data were identified by MEDLINE database search without publication date limitation.Expert opinionAn incomplete R1 finding may have no significant impact on a patient's clinical outcome, particularly in small G1 type I gastric NETs, which have an indolent course. A 'stepwise approach,' which uses more advanced endoscopic techniques, or minimally invasive surgery may be justified to achieve complete margin-free resection. This approach must balance the tumor features and the procedure-related risk of complications, particularly in the duodenum, where the role of deep endoscopic resections is limited due to the thin duodenal wall. Gastric and rectal NETs that are incompletely removed after initial resection are more easily amenable to deep endoscopic techniques. However, this might not be necessary for patients with comorbidities, elderly, or both due to the uncertainty of how R1 finding impacts a patient's clinical outcome.