All in all, dMMR/MSI CRCs without evident sporadic mechanisms (i.e., MLH1 promoter hypermethylation) and without germline mutation of MLH1, PMS2, MSH2, MSH6, deletion of EPCAM or germline MLH1 promoter hypermethylation are considered unclassified as regards the molecular mechanism underlying the MMR deficiency, LS versus sporadic cases. Here, MLH1 is linked to mismatch repair cancer syndrome 1.