Molecular classification and genetic pathways in hyperplastic polyposis syndrome.

Area of Science:

• Gastroenterology
• Oncology
• Molecular Biology

Background:

• Hyperplastic Polyposis Syndrome (HPPS) is a poorly understood condition associated with an increased risk of colorectal cancer (CRC).
• Current diagnostic criteria for HPPS are suboptimal and lack molecular classification.

Purpose of the Study:

• To establish a molecular classification for Hyperplastic Polyposis Syndrome.
• To investigate the molecular underpinnings of polyp formation in HPPS patients.

Main Methods:

• Analysis of 282 tumors from 32 putative HPPS patients, including hyperplastic polyps (HPs), adenomas, and CRCs.
• Somatic mutation analysis for BRAF and KRAS2, and microsatellite instability (MSI) testing.
• Comparison of mutation frequencies with sporadic HPs.

Main Results:

• No significant microsatellite instability (MSI) was detected in HPPS samples.
• Hyperplastic polyps (HPs) in HPPS patients showed monoclonal epithelium with frequent BRAF (two-thirds) or KRAS2 (10%) mutations.
• HPPS patients were classifiable into two groups based on BRAF or KRAS2 mutations in their polyps, suggesting distinct inherited predispositions.
• Adenomas and CRCs from HPPS patients generally lacked BRAF or KRAS2 mutations and did not predominantly follow the serrated pathway.

Conclusions:

• HPPS likely comprises distinct subtypes based on inherited predispositions influencing BRAF or KRAS2 mutation pathways.
• Molecular testing for BRAF, KRAS2, and MSI in polyps can improve HPPS diagnosis and differentiate it from sporadic HPs.
• A proposed molecular model could enhance HPPS case identification beyond current WHO clinical criteria.