In HER2-overexpressing breast cancer, which is associated with a high recurrence rate and poor outcome (Slamon et al, 1987; Paik et al, 1990; Kallioniemi et al, 1991; Boss et al, 2003), trastuzumab-based therapies are well established and regarded as a standard therapy (Slamon et al, 2001; Pegram et al, 2004). The gene discussed is ERBB2; the disease is breast cancer.