MLH1 and glioblastoma: However, the analysis of the tumor mutational load, mismatch repair (MMR) and immune checkpoint expression in glioblastoma (n = 198) revealed that only 3.5% of glioblastoma samples (seven of 198) had high tumor mutational load (DNA MMR mutations) associated with the loss of MLH1, MSH2, MSH6, and/or PMS2 expression [144].