CDKN2A and glioblastoma: Glioblastoma cells cultured in standard monolayer conditions in early passages tend to initially, at least in part, reflect both, genotype and phenotype (EGFRWT and EGFRvIII expression, CDKN2A copy number and expression of GFAP – a specific marker for astrocytes; Fig. 1d-e; Additional file 3: Table S3), as well as heterogeneity (presence of normal GFAP-negative cell populations) of the corresponding tissue specimens (Fig. 2a).