To evaluate the chromatin state of the CXCR4 promoter in Ewing sarcoma we performed ChIP-PCR studies using antibodies directed against the H3K4me3 and H3K27me3 histone modifications and genomic PCR primers specific for the CXCR4 promoter (Supplementary Figure S1A). Here, CXCR4 is linked to Ewing sarcoma.