ERBB2 and breast cancer: HER2 is amplified and overexpressed in 15–20% of breast cancers (Slamon et al, 1989), and also in a variety of other tumours such as ovarian carcinomas (Slamon et al, 1989), colorectal cancers (Al-Kuraya et al, 2007), gastric cancers, and oesophageal squamous cell carcinomas (ESCCs) (Takehana et al, 2002; Mimura et al, 2005).