Methylation patterns define two types of hyperplastic polyp associated with colorectal cancer

Area of Science:

• Gastroenterology
• Molecular Pathology
• Oncology

Background:

• Traditionally, hyperplastic polyps (HP) are considered non-neoplastic colorectal lesions.
• Emerging evidence links HP to colorectal cancer (CRC) pathogenesis, particularly those with DNA methylation and microsatellite instability.
• Identifying HP subtypes with neoplastic potential is crucial for risk stratification.

Purpose of the Study:

• To investigate morphological and molecular distinctions between different subtypes of colorectal hyperplastic polyps (HP).
• To identify specific features that may indicate a higher risk of neoplastic progression in HP.
• To understand the role of DNA methylation and genetic mutations in HP subtypes.

Main Methods:

• Comparison of HP adjacent to colorectal cancer (CRC) (Group I) with HP from individuals with hyperplastic polyposis (Group II).
• Analysis of DNA methylation patterns at specific loci (MINT 1, 2, 12, 31) and genes (HPP1, MGMT, p14ARF, p16INK4a, hMLH1).
• Assessment of K-ras mutations and morphological characteristics, including features of sessile serrated adenomas.

Main Results:

• Group II HP exhibited significantly higher DNA methylation across most tested loci compared to Group I HP.
• Group I HP displayed the lowest DNA methylation frequency but the highest K-ras mutation rate.
• HP variants in Group II shared morphological traits with sessile serrated adenomas, and hMLH1 methylation was frequent in dysplastic lesions within Group II.

Conclusions:

• Colorectal hyperplastic polyps demonstrate significant morphological and molecular heterogeneity.
• A distinct subset of HP, characterized by specific methylation patterns and morphology, possesses a notable potential for malignant transformation.
• These findings necessitate a re-evaluation of HP classification and risk assessment strategies.