MRC1 and colorectal carcinoma: The establishment of liver metastasis by HLA class I-negative tumour cell clones may be thwarted by the abundancy of NK cells in this tissue, as these innate lymphocytes play a fundamental role in recognising and eliminating cells with a “missing-self” phenotype.10 To further illustrate the difficulty of obtaining metastatic samples from MMR-d CRCs, we assessed the MMR status through immunohistochemical detection of PMS2 and MSH6 in 110 lung metastasis from CRC and failed to identify any MMR-d case (data not shown).