Here we show that the effects of ErbB2 on cell signalling kinetics are selectively associated with induction of apoptosis in oestrogen-responsive MCF7 human breast cancer cells – which, like most hormone-sensitive cancers (Caleffi et al, 1994; Elledge et al, 1995; Berns et al, 2000), express wild-type p53 (Casey et al, 1991; Balcer-Kubiczek et al, 1995; Furuwatari et al, 1998) but normally do not overexpress ErbB2 (Wright et al, 1997; Ferrero-Pous et al, 2000; Pinto et al, 2001). This evidence concerns the gene ERBB2 and breast cancer.