ERBB2 and breast neoplasm: HER2 overexpressing tumors (15–25% of breast tumors) are characterized, evidently, by increased expression of HER2 and HER2-associated genes, as well as genes linked to cell proliferation (36), and carry a worse prognosis than the luminal subtypes; however, with the advent of targeted treatment, survival has improved dramatically (19, 20, 37, 38).