Among the members of HER family, HER2 is overexpressed in 10–30% of patients with gastric cancer and is known to lead to a poor patient outcome owing to malignant progression, for example, metastasis and resistance to chemotherapy such as that found in breast cancer (David et al, 1992; Uchino et al, 1993). The gene discussed is ERBB2; the disease is breast carcinoma.