For this purpose we selected the Tg(flk1:GFP) zebrafish line, widely used for profiling of zebrafish vessel development (22–25, 38) (Figures 1A, B), as xenograft host for RMS cells fluorescently labelled with CM-Dil, to allow assessment of tumour burden (Figure 2C; Supplementary Figure 1A). The gene discussed is KDR; the disease is neoplasm.