From the time of the initial characterization of HER2 as an oncogenic receptor tyrosine kinase and a critical driver of HER2-positive disease, HER2 overexpression has been linked to several cancers including those affecting colorectal, gastric, lung, ovarian, and salivary gland tissues, as well as 15%–20% of breast cancers (1–5). This evidence concerns the gene ERBB2 and cancer.