MMR deficiency (dMMR) is triggered by germline, somatic, and epigenetic changes in MMR genes (most commonly MLH1, PMS2, MSH2, and MSH6), which inactivate these genes, causing loss of MMR-related protein expression, as noted by immunohistochemistry (IHC), and microsatellite instability (MSI) development (1–3). This evidence concerns the gene MRC1 and mismatch repair cancer syndrome 1.