Using PAX3-FOXO1 fusion oncogene positive rhabdomyosarcoma as a model system and a panel of HDAC inhibitors with diverse and well-characterized isoform selectivity, it was shown that Class I HDAC inhibitors were the most effective, followed by Class IIa (HDAC4/5/7/9), Class IIb (HDAC6/10), Class III (SIRT proteins), and Class IV (HDAC 11) [194]. Here, HDAC9 is linked to rhabdomyosarcoma.