pMMR (Proficient Mismatch Repair) and dMMR (Deficient Mismatch Repair) describe the status of the mismatch repair system, a crucial DNA repair mechanism in cells.
Here's a breakdown:
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pMMR (Proficient Mismatch Repair): This indicates that the mismatch repair system is functioning correctly. All four key MMR proteins (typically MLH1, MSH2, MSH6, and PMS2) are present and properly expressed. This means the cell can effectively identify and correct errors that occur during DNA replication.
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dMMR (Deficient Mismatch Repair): This indicates that the mismatch repair system is not functioning correctly. It means that one or more of the key MMR proteins (MLH1, MSH2, MSH6, or PMS2) are absent or not properly expressed. This deficiency leads to an accumulation of DNA replication errors and microsatellite instability (MSI), which can drive tumor development.
In diagnostic testing, immunohistochemistry (IHC) is often used to assess the expression of MMR proteins. If all four proteins are present, the sample is classified as pMMR. If any of the proteins are absent, it is classified as dMMR. dMMR status often leads to further testing such as Microsatellite Instability (MSI) testing.
In summary, pMMR indicates a functional mismatch repair system, while dMMR indicates a non-functional system due to the loss of one or more key MMR proteins. The status is crucial for cancer diagnosis, prognosis, and treatment decisions, particularly in cancers like colorectal and endometrial cancer.
