MMR testing, or Mismatch Repair testing, is a type of genetic test used to detect deficiencies in the mismatch repair (MMR) system of cells. This system is crucial for correcting errors during DNA replication. A deficiency in MMR can lead to an accumulation of mutations, increasing the risk of certain cancers, particularly colorectal and endometrial cancers. However, it's important to note that MMR testing also refers to a completely different test: a blood test for immunity to measles, mumps, and rubella (MMR) viruses. We will explore both meanings separately.
MMR Testing for Cancer Predisposition and Diagnosis
This type of MMR testing examines the genes responsible for mismatch repair. The most common genes tested include MLH1, MSH2, MSH6, PMS2, and EPCAM. These tests are primarily used for:
- Identifying Lynch syndrome (LS): A hereditary cancer predisposition syndrome characterized by increased risk of various cancers due to MMR defects. As noted in the provided text, MSI and/or MMR deficiency testing is traditionally performed in patients with colorectal (CRC) and endometrial cancer (EC) to screen for Lynch syndrome (LS).
- Determining treatment options: Especially in colorectal cancer, MMR status influences the effectiveness of certain immunotherapy treatments like pembrolizumab (KEYTRUDA®). The use of an FDA-approved test is recommended, as highlighted in the provided materials.
- Prognosis: Understanding the MMR status can help predict the course of the disease.
Two main methods are used to perform this type of MMR testing:
- Immunohistochemistry (IHC): This technique analyzes tumor tissue samples to determine the presence or absence of MMR proteins. IHC testing is performed to analyze colon and other tumor tissue samples to determine if the tumor is microsatellite unstable. Absence of one or more proteins suggests MMR deficiency.
- Microsatellite Instability (MSI) testing: This method looks for changes in short, repeated DNA sequences (microsatellites) within the tumor cells. MMR deficiency can be assessed by immunohistochemistry, checking for the presence or absence of the MMR proteins, with absence of one or more proteins indicating a deficiency. High levels of instability indicate MMR deficiency.
The National Comprehensive Cancer Network (NCCN) now recommends MMR deficiency testing for all colorectal cancer patients. The National Comprehensive Cancer Network (NCCN) now recommends all colorectal cancer patients receive a genetic test called a Mismatch Repair (MMR) Deficiency test. This highlights the clinical significance of this testing.
MMR Testing for Measles, Mumps, and Rubella (MMR) Immunity
This MMR test is a blood test used to determine immunity to measles, mumps, and rubella. It measures the levels of antibodies against these viruses. An MMR antibody screening is a single blood test that is used to help diagnose both measles and mumps or to see if you are immune. A high antibody titer indicates immunity, usually acquired through vaccination or previous infection. This test is often used to:
- Confirm immunity: To ensure individuals are protected against these diseases.
- Diagnose infections: While less common, it can assist in diagnosing measles or mumps infections in certain situations.
This test is readily available and can be purchased online and performed without a doctor's visit in some situations. Buy your own MMR immunity test online with Quest®. No doctor's visit is required – simply purchase, and access MMR titer testing at a nearby location.
In summary, the term "MMR testing" has two distinct meanings, one related to cancer genetics and the other to infectious disease immunity. It's crucial to understand the context to interpret results correctly.
