Interaction of Src with numerous breast cancer-associated growth factors and signalling pathways, such as prolactin (Acosta et al, 2003), EGFR (Biscardi et al, 2000), ERK1/2, PI3-kinase (Gaben et al, 2004), and oestrogen receptor (Migliaccio et al, 2005), supports the notion that Src activity contributes to the growth and survival of breast cancer cells. This evidence concerns the gene PRL and breast cancer.