CDKN2A and glioblastoma: In our series, 15 of 52 (28.8%) GBM harboring EGFR amplification presented a CT pattern affecting the EGFR locus (p < 0.0001) and 14/72 (19.4%) GBM with CDKN2A homozygous deletion displayed a CT pattern on chr 9p21 (p = 0.0003) (Figure 5).