Another group of HDACi-based radiopharmaceuticals, including [11C] trichostatin A, [11C]MS-275, [11C]KB631, [11C]4-phenylbutyric acid, [11C]valproate, [11C]butyric acid, [11C]CN89, [11C]CN107, [18F]F-panobinostat and [11C]PCI34051 demonstrated inadequate BBB penetration, which discourages their application for the HDAC-based imaging of GB, despite possible application in other tumor types [161,167,172,178,179,180,181]. Here, HDAC9 is linked to neoplasm.