MLH1 and neoplasm: dMMR can be diagnosed as classical two-protein losses (MLH1/PMS2, Figures 1A, B, or MSH2/MSH6 losses), non-classical single or multiple losses in >90% of tumor cells, or as unusual (focal/subclonal or heterogenous losses of >10% of tumor cells in the background of positive stromal cells [10, 15, 34–36] (Table 3; Figures 1C, D).