What is the percentage of malignancy in tubular (tubulous) and sessile polyps?

Malignancy Risk in Tubular and Sessile Polyps

Sessile polyps have a significantly higher risk of malignancy (approximately 10%) compared to tubular adenomas, which have a much lower risk of malignancy (typically less than 5%).

Risk of Malignancy by Polyp Type

Tubular Adenomas

• Tubular adenomas have the lowest risk of malignancy among adenomatous polyps
• According to large studies, tubular adenomas show:
  • Very low risk of malignancy in polyps <5mm (essentially 0%) 1
  • Approximately 4.4% risk of high-grade dysplasia in 6-10mm tubular adenomas 1
  • Higher risk (16.2%) of high-grade dysplasia in tubular adenomas >10mm 1

Sessile Polyps

• Sessile polyps carry a significantly higher risk of malignancy compared to pedunculated polyps
• The NCCN guidelines specifically note that patients with sessile polyps have approximately 10% risk of lymph node metastases, even when completely removed with favorable histological features 1
• Sessile shape is an independent risk factor for malignancy in large polyps 2
• Sessile polyps are more likely to have incomplete resection margins (18.3%) compared to pedunculated polyps (3.5%), further increasing risk 1

Risk Factors That Increase Malignancy Potential

Size

• Size is one of the most important determinants of malignancy risk:
  • Polyps >16mm have 4.27 times higher odds of submucosal invasion compared to polyps <5mm 1
  • Polyps >35mm have 10 times higher odds of submucosal invasion 1
  • Large polyps (≥31mm) have significantly higher malignancy rates (OR=1.500,95%CI:1.196-1.881) 2

Location

• Rectal location is an independent risk factor for malignancy (OR=1.253,95%CI:1.091-1.439) 2
• Malignant polyps are most commonly found in the sigmoid colon and rectum 1

Morphology

• Sessile serrated polyps have a higher risk of malignant transformation compared to traditional tubular adenomas 3
• Laterally spreading tumors with non-granular morphology (LST-NG) have higher risk of submucosal invasion (14%) compared to granular type (LST-G) (7%) 1

Clinical Implications

Management Considerations

• For pedunculated or sessile polyps with favorable histological features (grade 1-2, no angiolymphatic invasion, negative resection margin) and complete resection, no additional surgery is required 1
• However, for sessile polyps specifically, colectomy should be considered even with favorable histology due to the 10% risk of lymph node metastases 1
• Unfavorable histological features warranting surgical intervention include:
  • Grade 3 or 4 histology
  • Angiolymphatic invasion
  • Positive or indeterminate resection margin 1

Surveillance Recommendations

• All patients with resected polyps should undergo total colonoscopy to rule out synchronous polyps 1
• Patients with low-risk sessile serrated polyps have higher rates of advanced neoplasia upon surveillance (17.9%) compared to those with isolated low-risk tubular adenomas (7.8%) 3
• This suggests that surveillance intervals should be shorter for patients with sessile polyps

Special Considerations

Histological Assessment

• Tubulovillous/villous histology is associated with increased risk of advanced adenomas and neoplasia, but has not been included in UK post-polypectomy guidelines due to lack of inter-observer agreement among pathologists 1
• Proper specimen handling is crucial for accurate assessment of malignancy risk, especially for sessile polyps 1

Common Pitfalls

• Incomplete resection is more common with sessile polyps than pedunculated ones
• Fragmented specimens make margin assessment difficult, potentially leading to underestimation of malignancy risk
• Size estimation varies between in situ, pre-fixation, and post-fixation measurements, which can affect surveillance categorization 1
• Failure to recognize the higher risk of malignancy in sessile polyps may lead to inadequate follow-up and surveillance

In summary, sessile polyps carry approximately 10% risk of malignancy compared to the lower risk in tubular adenomas. Size, location, and morphology are important additional factors that influence malignancy risk and should guide management decisions.