CD8A and neoplasm: The main cause of microsatellite instability is the defective DNA mismatch repair function; once the repair mechanism is faulty, the cell will accumulate a large number of DNA mutations.[35] High mutagenicity can induce an increase of neoantigens in tumor cells, so EC induced by MSI-H/dMMR are more likely to be positive for tumor-infiltrating lymphocytes, such as PD1, CD8 + and cytotoxic T lymphocytes.