Previously, we have shown that in excess of 25% of IBD-CRCs are defective for mismatch repair, mostly as a result of MLH1 gene promoter hypermethylation, with a small number of mutations affecting any one of the four MMR genes, and these cancers, when metastatic, may also be considered for immune checkpoint inhibition based on the results of MMR immunohistochemistry [36], as shown here. This evidence concerns the gene MLH1 and inflammatory bowel disease.