MSI, or microsatellite instability, is a genetic alteration that occurs in some cancers. It refers to the instability of short, repetitive DNA sequences called microsatellites. These sequences are prone to errors during DNA replication, leading to insertions or deletions of nucleotides.
How does MSI occur?
MSI usually arises due to defects in DNA mismatch repair (MMR) genes. MMR genes are responsible for correcting errors that occur during DNA replication. When these genes are mutated, the DNA replication process becomes more error-prone, leading to MSI.
What does MSI mean in a biopsy?
If a biopsy reveals MSI, it suggests that the cancer may be more likely to respond to certain types of chemotherapy, particularly immunotherapy. MSI is also associated with a better prognosis in some cancers, such as colorectal cancer.
Examples of MSI in biopsies:
- Colorectal cancer: MSI is found in approximately 15% of colorectal cancers.
- Endometrial cancer: MSI is found in approximately 25-30% of endometrial cancers.
Importance of MSI testing:
MSI testing is becoming increasingly important in the management of cancer patients. It can help doctors:
- Determine the best treatment options.
- Predict the likelihood of response to immunotherapy.
- Estimate the prognosis of the cancer.
In summary, MSI is a genetic alteration that can be detected in biopsies and has important implications for cancer treatment and prognosis.
