ERBB2 and breast cancer: For example, trastuzumab, an anti-HER2 antibody, extends the overall lifespan for approximately 20% of breast cancer patients whose often-aggressive tumours overexpress ERBB2, the gene that encodes the HER2 protein.4 However, HER2-targeted therapies often result in treatment resistance and thus additional therapeutic targets are required to adequately treat HER2+ breast cancer, among other subtypes.