Considering that the zebrafish outperforms existing mouse models with respect to high-resolution imaging of the dynamic process of cell invasion during cancer progression, and is easily amenable to genetic and pharmacological screening, we therefore set out to investigate whether the xenograft breast cancer assay in zebrafish embryos can be used to determine the role of TGF-β signalling components in breast cancer invasion and metastasis. The gene discussed is TGFB1; the disease is cancer.