Expression of these receptors as well as unique gene expression patterns, identified through genomic profiling studies, can be used to further categorize breast cancer into at least five common subtypes: luminal-like subtypes A and B (expression of hormone receptors and luminal cytokeratins 8 and 18), basal-like (expression of cytokeratins 5 and 17 and typically no expression of hormone or HER2 receptors), HER2-positive or -enriched (mostly, but not all, HER2 amplified), and normal-like [3–5]. The gene discussed is ERBB2; the disease is breast cancer.