POLD1 and central nervous system cancer: A mean TMB of 13.9 mutations per megabase (mut/Mb) was identified in 14 glioma DNAs from 10 patients with rare POLE/POLD1 variants, with each TMB value higher than 2.6 mut/Mb, the median TMB in a study of 10,294 gliomas [32] (Fig. 3a).