What is MSI in Medical Terms?
MSI, in medical terms, most commonly refers to Microsatellite Instability. It's a condition found in some cancer cells where there are changes in the number of repeated DNA bases within microsatellites—short, repeated DNA sequences. This instability often arises from defects in DNA mismatch repair genes, leading to errors during DNA replication.
Microsatellite instability is not a cancer itself, but rather a characteristic of certain cancers. Its presence can have significant implications for cancer diagnosis, prognosis, and treatment planning.
- How it's detected: MSI is typically detected through testing that examines the microsatellite regions of a tumor's DNA. A high level of instability (MSI-H) indicates a significant number of errors in these repetitive sequences.
- Cancer Types: MSI is most frequently observed in colorectal, gastric, and endometrial cancers. However, it can be present in other cancers as well.
- Clinical Significance: The presence of MSI-H can influence treatment decisions. For instance, tumors with MSI-H often respond well to immunotherapy, particularly checkpoint inhibitors. The prognosis for some MSI-H cancers can also differ from those with microsatellite stable (MSS) cancers.
MSI-H Cancer: A Closer Look
MSI-H cancer (Microsatellite Instability-High cancer) specifically indicates a high level of microsatellite instability within the cancerous cells. This is a critical piece of information used in personalized cancer medicine.
- Treatment Implications: The information provided by MSI-H testing can be a powerful tool in selecting the most effective treatment for a patient. Immunotherapy, a type of cancer treatment that harnesses the body's own immune system to fight cancer, has shown significant promise in treating MSI-H cancers.
Sources: Information synthesized from multiple sources including the National Cancer Institute (NCI) Dictionary of Cancer Terms, MD Anderson Cancer Center, and Fight Colorectal Cancer. These sources consistently define MSI as Microsatellite Instability and highlight its relevance in cancer diagnostics and treatment.
