Fig. 3

Characterization of gliomas from patients with rare POLE/POLD1 germline variants with respect to features of defective polymerase proofreading by determining burden and signatures of somatic mutations as well as presence of multinucleated cells or enlarged nuclei. (a) Graph showing the tumor mutational burden (TMB), defined as the number of somatic coding non-synonymous mutations per megabase of coding DNA sequence (mut/Mb), of 14 gliomas from 10 patients with rare POLE/POLD1 variants. The threshold for hypermutation of 17 mut/Mb and the median TMB per glioma of 2.6 mut/Mb, as previously defined for gliomas [32], are shown as dashed or dotted lines. An astrocytoma CNS WHO grade 4 of a patient carrying a homozygous MSH6 germline frameshift variant served as positive control. (b) Graph showing the COSMIC database SBS signatures of somatic mutations of 14 gliomas from 10 patients with rare POLE/POLD1 germline variants, highlighting the contribution of POLE/POLD1 pathogenic variant and POLD1 pathogenic variant and MMR deficiency-associated signatures SBS10 and SBS20, MMR deficiency-associated signatures SBS6, SBS15, SBS21, and SBS26, and temozolomide treatment-associated signature SBS11. (c) Hematoxylin and eosin stained sections of four gliomas from patients with rare POLE germline variants showing enlarged nuclei (WI70-III.1 and WI207-III.1) or multinucleated cells (WI127-III.2 and WI104-III.1). Scale bar, 60 μm. A2/3/4, astrocytoma CNS WHO grade 2/3/4; CNS, central nervous system; GB4, glioblastoma CNS WHO grade 4; GS4, gliosarcoma CNS WHO grade 4; M, spinal metastasis; MMR, mismatch repair; O2, oligodendroglioma CNS WHO grade 2; P, primary tumor; R, recurrent tumor; WHO, World Health Organization