However, the clinical usability of a combined EGFR/HDAC-targeted approach might be limited due the fact that current clinical trials combining vorinostat, a class I/II HDAC inhibitor, with erlotinib, including one trial on recurrent glioblastoma (#NCT01110876), had to be terminated because of the unexpected toxicity of this combination of drugs [159]. This evidence concerns the gene HDAC9 and glioblastoma.