What is the management and work-up for invasive adenocarcinoma of the colon?

Management and Work-up of Invasive Adenocarcinoma in a Colon Polyp

The management of invasive adenocarcinoma in a colon polyp depends critically on whether the polyp was completely resected and whether favorable histologic features are present—if both criteria are met, observation alone is sufficient for pedunculated polyps, but sessile polyps warrant consideration of formal colectomy even with favorable features due to 10% risk of lymph node metastases. 1

Initial Pathology Review

Immediately review the pathology with a pathologist and surgeon to determine:

• Completeness of resection and margin status 1
• Polyp morphology (pedunculated vs. sessile) 1
• Tumor grade (1-4) 1
• Presence of angiolymphatic invasion 1
• Depth of invasion (confined to head, neck, stalk, or base) 1, 2

Mark the polyp site at colonoscopy if cancer is suspected, or within 2 weeks of polypectomy when pathology confirms invasive cancer. 1

Risk Stratification Based on Histologic Features

Favorable Histologic Features (Low Risk)

• Grade 1 or 2 differentiation 1
• No angiolymphatic invasion 1
• Negative resection margin (>1-2 mm from margin) 1
• Complete resection in single specimen 1

Unfavorable Histologic Features (High Risk)

• Grade 3 or 4 differentiation 1
• Angiolymphatic invasion present 1
• Positive margin (<1-2 mm from transected margin or tumor in diathermy zone) 1
• Fragmented specimen where margins cannot be assessed 1

Management Algorithm

For Pedunculated Polyps with Favorable Features

Observation alone is sufficient—no additional surgery required. 1 Pedunculated polyps with invasion confined to the head (Level 1), neck (Level 2), or stalk (Level 3) have minimal risk of lymph node metastases when completely resected with favorable features. 2

For Sessile Polyps with Favorable Features

Either observation OR colectomy with en bloc lymph node removal is appropriate. 1 This dual option exists because sessile polyps carry significantly higher risk of adverse outcomes including disease recurrence, mortality, and hematogenous metastasis compared to pedunculated polyps—approximately 10% risk of lymph node metastases even with favorable features. 1, 2 The higher risk stems from greater probability of positive margins after endoscopic removal. 1

For Any Polyp with Unfavorable Features

Formal colectomy with en bloc removal of regional lymph nodes is mandatory. 1 This includes:

• All pedunculated polyps with Level 4 invasion (base of stalk) 2
• All sessile lesions with any unfavorable feature 2
• Any fragmented specimen where margins cannot be assessed 1

Laparoscopic colectomy is an acceptable option when technical expertise is available. 1

Complete Staging Work-up for Invasive Cancer

All patients with invasive colon cancer appropriate for resection require:

• Pathologic tissue review 1
• Total colonoscopy to rule out synchronous polyps 1
• Complete blood count and chemistry profile 1
• Carcinoembryonic antigen (CEA) determination 1
• CT scans of chest, abdomen, and pelvis with intravenous contrast 1

PET/CT scan is NOT routinely indicated at baseline and should not be performed for general surveillance. 1 PET/CT may be considered only if CT or MRI shows suspicious but inconclusive abnormalities that would change management, but it does not replace contrast-enhanced diagnostic CT. 1 PET/CT cannot assess subcentimeter lesions as these are below detection threshold. 1

Contrast-enhanced MRI is the reference test for evaluating locally advanced tumors' relationship with surrounding structures or defining ambiguous liver lesions. 1

Surgical Principles for Formal Colectomy

The extent of colectomy should be based on tumor location, resecting the portion of bowel and arterial arcade containing regional lymph nodes. 1

At least 12 lymph nodes must be examined to establish stage II disease and avoid understaging. 1 Examination of fewer than 12 nodes is associated with suboptimal staging and potentially worse survival if necessary adjuvant treatment is not administered. 1

Additional nodes requiring biopsy or removal:

• Apical lymph nodes at the origin of the feeding vessel 1
• Any suspicious lymph nodes outside the field of resection 1

Resection must be complete (R0) to be considered curative—positive lymph nodes left behind indicate incomplete (R2) resection. 1

Post-Resection Surveillance and Follow-up

All patients who have resected polyps must undergo:

• Total colonoscopy to rule out synchronous polyps 1
• Appropriate surveillance endoscopy at 3-6 months postoperatively if not performed before surgery 1

Adjuvant chemotherapy is NOT recommended for patients with stage I lesions. 1

Critical Pitfalls to Avoid

Do not assume sessile polyps with favorable features are equivalent to pedunculated polyps—sessile morphology alone increases risk of adverse outcomes including 21% adverse event rate in one series versus 0% for pedunculated polyps. 2

Do not accept inadequate lymph node sampling—fewer than 12 nodes examined leaves patients suboptimally staged and potentially undertreated. 1

Do not order PET/CT scans routinely—this adds cost without benefit and does not replace diagnostic CT imaging. 1

Do not delay marking the polyp site—mark at time of resection or within 2 weeks to facilitate potential surgical resection. 1