Analysis of the expression of proteins of the unpaired base repair system using immunohistochemical reaction

Mismatch repair system is one of the mechanisms underlying maintenance of the genome integrity. It is involved in mitotic and meiotic recombination, apoptosis, immune globulin gene rearrangement, somatic hypermutation and other processes. Deficiency of mismatch repair system (d-MMR) occurs in most types of tumors, it leads to hypermutability and microsatellite instability. Recognition of mismatch repair system deficiency or microsatellite instability is used for diagnostic, predictive, and prognostic purposes, in particular to screen for Lynch syndrome and identify patients who will respond to checkpoint inhibitor therapy, as well as for prognostic evaluation of clinical course. In the present article, we provide a brief overview of practical methods to recognize deficiency of mismatch repair system, focusing on clinical testing using immunohistochemical reaction and results’ interpretation.

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