Microsatellite Instability (MSI)

What is Microsatellite Instability (MSI) by IHC test?

Microsatellite Instability (MSI) by IHC test used to screen for Microsatellite Instability (MSI) and Mismatch Repair (MMR) deficiency in tumor tissues. MSI by IHC checks for the presence or absence of four key MMR proteins: MLH1, MSH2, MSH6 and PMS2. Loss of one or more of these proteins suggests deficient mismatch repair (dMMR) and high MSI (MSI-H) status — a key feature of some colorectal, endometrial, and gastric cancers. It is used to identify Lynch syndrome and assess cancer risk.

Why consider is Microsatellite Instability (MSI) by IHC test?

• To identify patients with MSI-H or dMMR tumors, which may respond better to immunotherapy (e.g., PD-1 inhibitors) and indicate Lynch Syndrome (a hereditary cancer syndrome)
• Helps guide treatment choices and assess prognosis
• Useful as a screening tool in colorectal and endometrial cancers

Who should get tested for Microsatellite Instability (MSI) by IHC test?

• Patients diagnosed with colorectal, endometrial, or gastric cancer
• Individuals with family history of Lynch syndrome or early-onset cancers
• Tumors with unusual histology or poor differentiation

More Information

OTHER NAMES: IHC for Mismatch Repair Proteins, IHC MSI Panel (MLH1, MSH2, MSH6, PMS2), MSI Screening by IHC, Lynch Syndrome Screening Test, dMMR Detection by Immunohistochemistry

Microsatellite Instability (MSI) is a condition of genetic hypermutability resulting from a defective DNA mismatch repair (MMR) system. When the MMR system is impaired, errors that normally occur during DNA replication—especially in short repetitive DNA sequences called microsatellites—are not corrected, leading to instability. Cancers commonly associated with MSI: Colorectal cancer, Endometrial (uterine) cancer, Gastric cancer, Ovarian cancer, Small intestine cancer