MRC1 and colorectal carcinoma: To estimate the minimum MMR deficient tumor cell content required for a CRC to be classified as MSI‐H, we mixed DNA from HCT116 (a clonal, MMR deficient CRC cell line) with DNA from nonneoplastic PBLs to create, in triplicate, sample mixtures containing 0.78–100% DNA from MSI‐H cells.