What is the next management step for a 78-year-old patient with a rectal neuroendocrine tumor (NET) and positive lateral resection margins after endoscopic submucosal dissection (ESD)?

Management of Rectal Neuroendocrine Tumor with Positive Lateral Margins After Endoscopic Submucosal Dissection

Referral for completion total mesorectal excision (TME) is the most appropriate next management strategy for this patient with a pT2 rectal neuroendocrine tumor with positive lateral margins and lymphovascular invasion after endoscopic submucosal dissection.

Rationale for TME Recommendation

Pathological Risk Assessment

The patient's case presents several high-risk features that warrant more aggressive management:

• pT2 tumor (invasion into muscularis propria)
• Positive lateral resection margins at the 3 o'clock position
• Evidence of lymphovascular invasion in multiple areas
• Large tumor size (6 cm)

According to ESMO guidelines, T2 rectal tumors should be treated by radical TME surgery because of higher risks of recurrence and higher risk of mesorectal lymph node involvement 1. The presence of lymphovascular invasion significantly increases the risk of lymph node metastasis, despite the tumor being a well-differentiated NET G1.

Why Other Options Are Insufficient

1. Surveillance alone (Option A) is inadequate given the positive margins and lymphovascular invasion. These features indicate a high risk of local recurrence and potential metastatic spread.

2. Repeat endoscopic resection (Option B) is unlikely to be successful because:

   • The tumor has already invaded the muscularis propria (pT2)
   • The initial procedure was technically challenging (4.5 hours)
   • Full-thickness removal was already performed in several areas
   • The positive lateral margin likely indicates residual disease that may not be amenable to further endoscopic management

3. Adjuvant somatostatin analog therapy (Option D) alone would not address the local disease control needed with positive margins and lymphovascular invasion.

Management Algorithm

1. Immediate next step: Refer for completion TME surgery

   • This provides the best chance for complete oncological clearance
   • Allows proper lymph node evaluation and removal
   • Addresses the positive lateral margins and lymphovascular invasion risk

2. Post-TME considerations:

   • Pathological evaluation of the surgical specimen to determine if there is residual tumor
   • Assessment of lymph node status
   • If positive lymph nodes are found, consider adjuvant therapy

3. Follow-up after definitive treatment:

   • Clinical assessment every 6 months for 2 years 1
   • Completion colonoscopy within the first year
   • Regular imaging surveillance with CT chest/abdomen/pelvis

Special Considerations for This Patient

While the patient has expressed a preference to avoid major pelvic surgery and has medical comorbidities (CAD, CKD stage 3, mild cognitive impairment), the high-risk features of the tumor make TME necessary for optimal oncological outcomes. The risk of local recurrence and metastatic spread with positive margins and lymphovascular invasion outweighs the risks of surgery.

Potential Pitfalls to Avoid

1. Underestimating the significance of positive margins: Positive lateral margins after ESD for rectal NETs are associated with high local recurrence rates.

2. Overlooking lymphovascular invasion: This is a strong predictor of lymph node metastasis, even in well-differentiated NETs.

3. Relying solely on the low Ki-67 index: While the tumor is G1 (Ki-67 1.5%), the positive margins and lymphovascular invasion override the favorable grade in decision-making.

4. Delaying definitive management: Prompt completion TME provides the best chance for cure before potential metastatic spread occurs.

In conclusion, despite the patient's preference to avoid major surgery, the pathological findings after ESD clearly indicate the need for completion TME to ensure the best long-term oncological outcome and quality of life by preventing local recurrence and metastatic disease.