Sporadic colorectal carcinomas with low-level microsatellite instability in Korea: Do they form a distinct subgroup with distinguished clinicopathological features?

Background: The biologic significance of low-level microsatellite instability (MSI) in colorectal cancers (CRCs) remains unclear. This study aimed to elucidate whether sporadic MSI-low CRCs in Korea displayed distinguished clinicopathological characteristics from microsatellite stable (MSS) and MSI-high CRCs. Methods: We consecutively enrolled 657 patients who underwent their first surgical resections for stage I-IV sporadic CRCs and compared their clinicopathological features and prognosis after resection according to MSI status (574 MSS, 30 MSI-low and 53 MSI-high CRCs). Results: When compared with MSS CRCs, MSI-low CRCs showed significantly more frequent association with poorly differentiated histology, mucinous carcinoma, and large tumour size. In addition, MSI-low CRCs demonstrated significantly less frequent lymph node metastasis and advanced tumour stage than MSS CRCs. When compared with MSI-high CRCs, MSI-low CRCs were significantly more frequently located in distal colon. Three-year overall and disease-free survival rates of MSS, MSI-low and MSI-high CRCs were 83.5%, 90.0% and 91.7% and 82.0%, 89.1% and 87.5%, respectively and neither demonstrated significant difference between three groups. Conclusions: These results indicated that sporadic MSI-low CRCs in Korea displayed distinguished clinicopathological features and might form a distinct subgroup especially from MSS CRCs. Further large studies are required to evaluate the impact of MSI-low status on prognosis.