Treatment of Rectal Grade 1 Neuroendocrine Tumour
For rectal grade 1 neuroendocrine tumours ≤1 cm, endoscopic or transanal excision is the definitive treatment, with no follow-up required due to excellent prognosis. 1
Treatment Algorithm Based on Tumor Size
Tumors <1 cm
- Endoscopic or transanal excision is curative and sufficient 1
- Modified endoscopic mucosal resection is the preferred technique for tumors <10 mm, as it is effective, safe, relatively simple, and less time-consuming compared to endoscopic submucosal dissection 2
- No follow-up is required after complete resection - the prognosis is excellent with essentially 0% risk of metastasis 1, 3
- Recent evidence confirms that G1 NETs up to 20 mm have no lymph node or distant metastases during long-term follow-up (median 11.6 years) 3
Tumors 1-2 cm
- Endoscopic or transanal excision remains the primary approach 1
- Pre-resection staging with examination under anesthesia and/or endoscopic ultrasound (EUS) should be performed given higher invasion risk 1
- Follow-up endoscopies with rectal MRI or EUS at 6 and 12 months after resection, then as clinically indicated 1
- Endoscopic submucosal dissection should be considered when tumor size is >10 mm, particularly if suctioning is not possible due to fibrosis or if snaring for modified endoscopic mucosal resection does not work well 2
- Recent data shows endoscopic resection of 1-1.5 cm grade 1 rectal NETs yields comparable outcomes to tumors <1 cm, with 97.2% negative resection margins and no recurrence during 54-month median follow-up 4
Tumors >2 cm or High-Risk Features
- Low anterior resection or (rarely) abdominoperineal resection is required 1
- Surgical resection is mandatory for tumors with:
Critical Staging Before Treatment
Pre-treatment evaluation must include:
- Endoscopic ultrasound to assess depth of invasion and lymph node involvement 1
- Examination under anesthesia for tumors 1-2 cm 1
- Abdominal/pelvic CT or MRI if incomplete resection or tumors >2 cm to exclude distant metastases 1
Important Caveats and Pitfalls
Lymphovascular invasion changes management: Even in tumors 6-10 mm, the presence of lymphovascular invasion carries metastatic risk equivalent to adenocarcinomas and necessitates radical surgery with regional lymph node dissection 5. One case series documented lymph node metastasis in a 6-10 mm tumor with lymphovascular invasion 5.
Histologic examination is mandatory: All endoscopically resected specimens must be examined for lymphovascular invasion to determine if further radical surgery is needed 5. This is not covered by WHO 2010 guidelines but is critical for clinical decision-making 5.
Complete resection is essential: Incomplete resection margins require restaging and consideration of surgical resection 1. The goal is R0 resection with negative margins 4.
Grade matters: While this question specifies grade 1, note that all three cases with metastases in the Dutch nationwide study were grade 2 tumors 3. Grade 2 tumors require more aggressive management 3.