CDKN2A and glioblastoma: However, some exceptions could be observed: TP53 and PIK3CA were mutated in ~ 30–40% of the samples, FGFR3/4 were almost exclusively amplified in a subgroup of breast and squamous malignancies (head and neck and lung squamous cancers), and CDKN2A/B deletions clearly defined a subgroup of glioblastoma samples mixed with lung and head and neck samples.