Molecular differences between sporadic serrated and conventional colorectal adenomas

Area of Science:

• Gastroenterology
• Molecular Biology
• Oncology

Background:

• Serrated adenomas (SAs) represent a distinct pathway of colorectal neoplasia.
• Understanding the molecular differences between SAs, conventional adenomas (CADs), and hyperplastic polyps (HPs) is crucial for risk stratification and management.

Purpose of the Study:

• To compare the molecular characteristics of serrated adenomas (SAs) with conventional adenomas (CADs) and hyperplastic polyps (HPs).
• To investigate the roles of genetic instability and specific gene mutations in SA tumorigenesis and progression.

Main Methods:

• Evaluation of proliferative activity using Ki-67 expression in 47 SAs, 71 CADs, and 23 HPs.
• Analysis of KRAS, p53, BRAF, and RAS mutations across the three histological groups.
• Microsatellite instability (MSI) analysis and assessment of hMLH-1 expression in SAs, CADs, and HPs.

Main Results:

• SAs exhibited intermediate proliferative activity between CADs and HPs.
• Microsatellite instability-high (MSI-H) was significantly more frequent in SAs (21%) than in CADs (5%) or HPs (8%), especially in pure-type SAs (36%).
• BRAF or KRAS mutations were present in 49% of SAs, independent of MSI-H status, suggesting a parallel pathway in tumor progression.

Conclusions:

• Genetic instability is a key feature in the tumorigenesis of serrated adenomas, particularly pure-type SAs.
• Activation of the Ras/Raf/MEK/MAP kinase pathway via BRAF or KRAS mutations is implicated in the progression of approximately half of SAs, irrespective of genetic instability.
• These findings highlight distinct molecular mechanisms driving SA development and progression.