Microsatellite Instability: NPCC/Lynch Syndrome
Polymerase chain reaction/DNA fragment analysis
Monday - Friday
5 - 10 business days
This test is used to diagnose carcinomas associated with microsatellite instability (MSI), such as those in HNPCC/Lynch syndrome.
Paraffin-embedded tissue; send tissue blocks that contain normal and tumor tissues to the lab. In case the blocks are not available, 5 unstained slides of each tissue types are accepted. Ship the specimen at 20° - 25° C. Tissues fixed in formalin substitute are unacceptable. A tumor region with less than 50% of tumors is not acceptable.
Blood or buccal cells can be accepted as normal control of the MSI study. Ship 3 mL of blood in EDTA (purple-top tube) or ACD (yellow-top tube) at 4° C. Severely hemolyzed whole blood or clotted/ frozen blood/bone marrow specimen is not accepted.
- MSI-High: This patient has a tumor with two or more unstable microsatellite markers
- MSI-Low: This patient has a tumor with one unstable microsatellite markers
- MSI-Stable: This patient has a tumor with no detectable instability.
Microsatellite instability high (MSI-H) indicates a significant level of microsatellite instability in a tumor. MSI-H is present in more than 90% of patients with hereditary non-polyposis colorectal cancer (HNPCC) and in 15 - 20% of sporadic colorectal tumors. Genetic counseling and/or germ-line mutation analysis of mismatch-repair genes (MSH2, MLH1, and MSH6) are recommended to the patient/family with microsatellite instability-high tumors and a high suspicion of HNPCC.
MSI-low or MSI stable indicates no significant genomic microsatellite instability in a tumor. Stable genomic microsatellites would be rare in hereditary nonpolyposis colorectal cancer; however, it does not completely exclude the possibility of that or other inherited syndromes. Correlate with clinical findings or genetic counseling is recommended. This interpretation may not apply to cancers other than colon cancers.