Abstract The paired box transcription factor (PAX) family consists of 9 highly related members with critical roles in organogenesis and tissue specification during development, including skeletal muscle, pancreas, central nervous system, kidney, and immune system. In various cell model systems, PAX genes have been implicated in the maintenance of the multipotent state, the initiation of differentiation programs, cell migration, proliferation and survival. Mutations and gene rearrangement of PAX genes are frequently associated with human diseases and cancers. In particular, PAX3 and PAX7 are required during early embryogenesis for the development of the neural-crest and skeletal muscle, and gene rearrangements with FKHR are frequently implicated with rhabdomyosarcoma (RMS). The PAX3-FKHR fusion protein is present in the majority of alveolar rhabdomyosarcoma (ARMS) associated with increased aggressiveness and poor prognosis. To better understand the molecular pathogenesis of PAX3-FKHR, we carried out the first and unbiased genome-wide identification of PAX3-FKHR binding sites and associated target genes in ARMS, with a novel monoclonal antibody specific for the fusion protein. The data shows that PAX3-FKHR binds to the same sites as PAX3 at both MYF5 and MYOD enhancers. The genome-wide analysis reveals that the PAX3-FKHR sites are: 1) mostly distal to transcription start sites; 2) conserved; 3) enriched for PAX3 motifs; and 4) strongly associated with genes over-expressed in PAX3-FKHR positive RMS cells and tumors. There is little evidence in our dataset for PAX3-FKHR binding at the promoters. The genome-wide analysis further illustrates a strong association between PAX3 and E-box motifs in these binding sites, suggestive of a common co-regulation for many target genes. We further provide the first direct evidence that FGFR4 and IGF1R are the targets for PAX3-FKHR. The study is the first genome-wide analysis of direct targets for a PAX protein. The map of PAX3-FKHR binding sites provides the frame work for the understanding of PAX3-FKHR pathogenic roles and molecular targets to allow a systematic evaluation of agents against this aggressive RMS. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5344. doi:10.1158/1538-7445.AM2011-5344