The upregulated ErbB2-induced homodimerization enhances its tyrosine-phosphorylation and the activation of at least the same three signalling pathways as those downstream of ErbB1 for cell proliferation, survival, and migration, eventually leading to cancer cell tumourigenesis, invasiveness, and metastasis1–5,27–32(Fig. 1b). This evidence concerns the gene ERBB2 and cancer.