A rational approach to the evaluation of these new anti-ErbB2 immunoagents as potential antitumour agents is the comparison of their properties with those of Herceptin (trastuzumab), now established as a powerful therapeutic tool for ErbB2-overexpressing breast cancer, and other carcinomas (Stebbing et al, 2000; Scholl et al, 2001). The gene discussed is ERBB2; the disease is breast cancer.