Rectal neuroendocrine tumors: Update

Table 1 International guidelines for management of rectal neuroendocrine tumors

Guidelines	Treatment recommendations
European Neuroendocrine Tumor Society, 2023[76]	For lesions ≤ 10 mm: Endoscopic resection such as mEMR, ESD, and eFTR is recommended and recurrence rates are low
	For lesions ≥ 20 mm: Initial assessment is performed using EUS and pelvic MRI for local staging. Distant metastases staging is done using chest and abdominal CT/MRI and 68Gallium-SSA-PET-CT. For positive lesions Surgical resection using LAR or APR is recommended (after exclusion of unresectable distant metastases)
	For lesions 10-20 mm: Initial assessment is performed using EUS and pelvic MRI for local staging. Distant metastases staging is done using chest and abdominal CT/MRI and 68Gallium SSA-PET-CT. For positive lesions, either endoscopic or definitive surgical therapy is decided through multidisciplinary team discussions
National Cancer Comprehensive Cancer Network, 2025[77]	Very small (< 1 cm)
	Negative margin: No further follow-up
	Indeterminate margin: Classification into low grade (G1) that requires endoscopy follow up (6-12 months) and referral to the pathway below (all other tumor sizes) if positive or intermediate grade (G2)
	All other tumor sizes
	T1 stage: Resection (endoscopic or transanal)
	Lesions less than 1 cm with no follow up
	Lesions follow up every 6-12 months
	Management depends on the size for T2-T4 stages: Comprehensive assessment by colonoscopy, multiphasic imaging CT scan/MRI, Chest CT scan, SSTR PET-CT or SSTR PET-MRI and biochemical evaluation as clinically indicated
	Size ≤ 2 cm: Resection by endoscopy or transanal surgery; if size < 1 cm, no further follow up is needed; if 1-2 cm, frequent (6-12 months) follow up by endoscopy or MRI
	Size > 2 cm or presence of positive lymph nodes: Low anterior resection, abdominoperineal resection, or Neoadjuvant or definitive chemoradiation. Aim for cytoreduction
	Metastatic lesions: Management with aim of cytoreduction
Polish Network of Neuroendocrine Tumors, 2022[78]	Size < 1 cm with no risk factors: Endoscopic resection
	Size 1-2 cm with no risk factors: Endoscopic resection
	Size 1-2 cm with risk factors: Surgical treatment using: (1) Transanal approach with either Transanal endoscopic microsurgery or through the open rectum access; (2) Laparoscopic approach with either abdominoperineal amputation of the rectum or anterior resection of the rectum; and (3) Through open access with either abdominoperineal amputation of the rectum or anterior resection of the rectum
	Risk factors to consider include: Infiltration of the muscular membrane proper, involvement of regional lymph nodes, infiltration of lymphatic and/or blood vessels, and a proliferation index above 2%

T1 means tumor invades the lamina propria or submucosa; T2 means tumor invades the muscular layer or is 2 cm in size; T3 means tumor invades into subserosal tissue; T4 means tumor invades serosa and/or adjacent organs (American Joint Committee on Cancer (AJCC) 8^th edition)[79]. mEMR: Modified endoscopic mucosal resection; ESD: Endoscopic submucosal dissection; eFTR: Endoscopic full-thickness resection; MRI: Magnetic resonance imaging; CT: Computed tomography; SSA: Somatostatin analogues; EUS: Endoscopic ultrasound; PET: Positron emission tomography; LAR: Low anterior resection; APR: Abdominoperineal resection; SSRT: Somatostatin receptor.