TERT and oligodendroglioma: Sanger sequencing of the TERT promoter region was performed (i) for all WGS samples having only low coverage in the promoter sequence (below 40×, n = 6, Supplementary Fig. 10g), (ii) the FFPE extension cohort, and (iii) three oligodendrogliomas, known to carry high frequency TERT promoter mutation139.