In a preliminary study, the promoter usage of the MDM2 gene was also investigated in a series of primary astrocytic tumours, comprising of 45 GBs, 5 AAs and 5 As (Supplementary Table 1) as well as in two additional glioblastoma cell lines (CCF-STTG1 and Tp365MG) and 3 glioblastoma xenografts (GB217X4, GB181X13 and GB166X1) with known MDM2, TP53 and p14ARF gene status using promoter-specific primers. Here, TP53 is linked to glioblastoma.