One of the most successful examples of the molecular biomarker approach is trastuzumab, also known as Herceptin (Genentech).2 The FDA approved trastuzumab for the treatment of metastatic breast cancer in 1998 (Ignatiadis et al. 2009), and it has been heralded as having a profound impact on the care of HER2+ breast cancers3 (Hudis 2007), and as “a major advance in targeted cancer therapies” (National Breast Cancer Coalition 2013). This evidence concerns the gene ERBB2 and breast cancer.