Thus far, there are at least five molecularly defined subtypes, which can also categorize subtypes of breast cancers and these are luminal-A, luminal-B, Her2, basal-like, and claudin-low; it is unclear whether the controversial normal-like represents a true molecular subtype or merely a contamination of breast tumor specimens with normal mammary tissue [13–16]. The gene discussed is ERBB2; the disease is breast cancer.