MSI by IHC

General Information

Lab Name

Lab Code

669

Description

For MSI PCR testing see separate test (Microsatellite Instability DNA test, mnemonic "MSI"). MSI testing by immunohistochemistry measures the presence or absence of immunoreactivity for MLH1, PMS2, MSH2 and MSH6 mismatch repair gene products in tumor tissue. One advantage of this form of testing over PCR-based microsatellite instability testing is that the results suggest which gene products are involved. DNA sequencing of the affected gene(s), such as with the ColoSeq™ Lynch and Polyposis panel is needed confirm an underlying genetic abnormality. MLH1/PMS2 and MSH2/MSH6 are typically expressed together as functional units meaning that MLH1/PMS2 and MSH2/MSH6 immunoreactivity is often lost together when absent. Isolated loss of either PMS2 or MSH6 is typically due to a mutational event and is correlated with Lynch syndrome (HNPCC). Loss of MLH1 expression is most commonly due to promoter methylation. Patients with Lynch syndrome frequently are positive for BRAF mutations and negative for MLH1 promoter hypermethylation in tumor tissue. Additional testing for MSI by PCR, BRAF mutations and/or MLH1 promoter hypermethylation may have utility in some cases. This testing is performed in Pathology's Immunohistochemistry Laboratory. Please call (206) 598-4202 for information. Or check the Pathology website found at: Pathology's Immunohistochemistry

Synonyms

colon cancer, hMLH1, hMSH2, hMSH6, HNPCC, ICC, IHC, immunohistochemistry, ip msi, Lynch syndrome, microsatellite instability, MLH1, MSH2, MSH6, MSI, Muir-Torre, PMS2