In immunohistochemical analysis, the three tumours derived from patients carrying mutations R128L, K728T, and G881K+S, expressed MSH6 but lacked MLH1 protein, which may explain the MSI phenotype in these tumours and suggests IHC staining for the MLH1 protein as the first approach in microsatellite unstable tumours. Here, MLH1 is linked to neoplasm.