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Colorectal carcinogenesis: MSI-H versus MSI-L
Timothy M Pawlik1, Chandrajit P Raut, Miguel A Rodriguez-Bigas
1Department of Surgical Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
Disease Markers
|November 6, 2004
Summary
Microsatellite instability-high (MSI-H) colorectal cancers have distinct features and better prognoses, often due to MLH1 silencing. The existence of a separate MSI-low (MSI-L) group remains debated, potentially differing quantitatively, not qualitatively, from microsatellite stable tumors.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Microsatellite instability (MSI) is a hallmark of hereditary non-polyposis colorectal syndrome and occurs in 10-15% of sporadic colorectal cancers.
- MSI phenotypes include MSI-high (MSI-H) and MSI-low (MSI-L).
- MSI-H sporadic colorectal cancers exhibit distinct clinicopathologic features and a better long-term prognosis, often linked to MLH1 epigenetic silencing.
Purpose of the Study:
- To delineate the characteristics and potential distinctness of MSI-low (MSI-L) colorectal tumors compared to microsatellite stable (MSS) tumors.
- To explore the molecular pathways and clinical significance of different MSI phenotypes in colorectal cancer.
Main Methods:
- Analysis of clinicopathologic features and molecular markers in MSI-H, MSI-L, and MSS colorectal tumors.
- Review of existing literature on the genetic and epigenetic alterations associated with MSI phenotypes.
Main Results:
- MSI-H tumors present a well-defined group with favorable prognosis, frequently associated with MLH1 gene silencing.
- MSI-L tumors have not consistently shown distinct clinicopathologic or molecular features compared to MSS tumors.
- MSI-L tumors may arise via the chromosomal instability pathway, similar to MSS tumors, with ongoing debate regarding their qualitative distinctness.
Conclusions:
- Sporadic MSI-H colorectal cancer is a distinct entity with a better prognosis, primarily driven by MLH1 silencing.
- The existence and distinctness of MSI-L colorectal cancer as a separate group from MSS tumors remain uncertain, suggesting potential quantitative rather than qualitative differences.
- Further research is needed to identify specific mutations in non-MSI-H tumors to potentially sub-classify MSI-L tumors and elucidate subtle differences from MSS tumors.