Risk factors for residual tumors in histologically incompletely resected rectal neuroendocrine tumors.

Background: Rectal neuroendocrine tumors (r-NETs) are often misidentified as polyps, leading to inappropriate endoscopic treatment and incomplete resection.

Aims: This study investigated the occurrence and risk factors of residual r-NETs following salvage local resection (SLR) after incomplete resection.

Methods: The medical records of 95 patients who underwent SLR for histologically incompletely resected (R1/Rx-resected) r-NETs referred from other hospitals between January 2020 and August 2023 were analyzed.

Results: The residual r-NET rate was 48.4 % (46/95), varying according to the primary resection method: cold forceps polypectomy (CFP), 70.0 % (21/30); conventional polypectomy or endoscopic mucosal resection (EMR), 41.7 % (25/60); and modified EMR or endoscopic submucosal dissection, 0 % (0/5). The residual r-NET rate was 65.7 % for endoscopically incomplete primary resection versus 0 % for endoscopically complete primary resection. Upon multivariate analysis, endoscopically suspected remnant tumors before SLR (odds ratio [OR], 15.56; 95 % confidence interval [CI], 2.94-82.35, p = 0.002) and the use of CFP for primary resection (OR, 3.60; 95 % CI, 1.02-14.52, p = 0.043) were associated with residual r-NETs after SLR.

Conclusion: Salvage resection should be considered for R1/Rx-resected r-NET cases with risk factors for residual tumors to lower the likelihood of recurrence.