HDAC9 and neuroblastoma: Selective for HDAC class I and II, several pre-clinical trials have noted the effectiveness of 4PB in neuroblastoma, reducing proliferation, inducing differentiation and impairing tumor growth and metastasis in vitro and in vivo. Cytotoxic in combination with vincristine in vitro (Pelidis et al., 1998) and enhances the expression of favorable marker genes (Tang et al., 2004).