Hepatocyte growth factor/scatter factor and its receptor, the tyrosine kinase Met, arose late in evolution and are unique to vertebrates. In spite of this, Met uses molecules such as Gab1 - homologues of which are present in Caenorhabditis elegans and Drosophila melanogaster for downstream signalling. Pivotal roles for Met in development and cancer have been established: Met controls cell migration and growth in embryogenesis; it also controls growth, invasion and metastasis in cancer cells; and activating Met mutations predispose to human cancer.