Microsatellite instability and the clinicopathological features of sporadic colorectal cancer

Area of Science:

• Oncology
• Molecular Biology
• Pathology

Background:

• Sporadic colorectal cancer (CRC) encompasses a heterogeneous group of tumors.
• The microsatellite instability (MSI) phenotype is a key molecular characteristic influencing CRC behavior.
• Effective identification of MSI-H CRC in routine pathology is crucial for clinical management.

Purpose of the Study:

• To prospectively evaluate the clinical significance of the MSI phenotype in sporadic CRC.
• To investigate reliable methods for identifying MSI-H tumors in routine pathology practice.

Main Methods:

• DNA analysis using polymerase chain reaction (PCR) to determine microsatellite status in 310 sporadic CRC tumors.
• Immunohistochemistry (IHC) to assess the expression of MLH1, MSH2, and p53 proteins.
• Correlation of MSI status with histopathological features and patient survival.

Main Results:

• 11% of tumors exhibited high-level microsatellite instability (MSI-H), and 6.8% showed low-level instability (MSI-L).
• MSI-H tumors were associated with higher grade, mucinous phenotype, increased intraepithelial lymphocytes, right-sided location, female predominance, and improved overall survival.
• Loss of MLH1 (8%) or MSH2 (1%) expression was observed, with IHC demonstrating >95% positive and negative predictive value for MSI-H detection.

Conclusions:

• The MSI-H phenotype defines a distinct pathological and clinical subtype of sporadic CRC.
• Immunohistochemical staining for MLH1 and MSH2 is an accurate and cost-effective method for identifying MSI-H tumors in routine pathology.
• This identification facilitates tailored clinical management and prognostic assessment for patients with sporadic CRC.