DNA mismatch repair proteins: scientific update and practical guide.

DNA mismatch repair (MMR) proteins are essential for the recognition and correction of sporadic genetic mutations that occur during DNA replication. Deficient MMR function (dMMR) leads to an increased risk of development of neoplasia. Identification of dMMR within tumours can suggest a high chance of the inherited cancer condition Lynch syndrome and predicts poor clinical response to certain conventional chemotherapies but an increased likelihood of response to immunotherapy. This review provides an update on the biology of MMR proteins, their encoding genes and mechanisms for the development of dMMR. This is followed by a discussion of the identification and significance of dMMR in routine clinical practice.