This allows for the definition of cut-off values for reliable detection of mutations, even at low MAFs, and the distinction of different levels of copy number variations, such as the diagnostically relevant distinction between low-level gain from high-level gain (amplification) of the EGFR gene in IDH-wildtype glioblastomas, and homozygous from hemizygous deletion of the CDKN2A gene in IDH-mutant astrocytomas. The gene discussed is CDKN2A; the disease is glioblastoma.