Many of the most efficacious recent drugs target specific genetic aberrations rather than histological disease subtypes, for example trastuzumab and lapatinib for treating HER2-positive breast cancers [1], tamoxifen for treating ER-positive breast cancers[2,3], and gefitinib and erlotinib for non-small cell lung cancer with EGFR mutations [4-8]. This evidence concerns the gene ERBB2 and breast cancer.