CXCR4 and osteosarcoma: Preliminary microarray results showed that CXCR4 and interesting chemokine ligands like CXCL1, -2, -3, and -5 are only highly expressed in clinical samples and not in xenografts or cell lines (Namløs et al., unpublished data), a finding supported by a previous study of osteosarcoma patient samples and cell lines [24].