Specifically, ERBB2+ breast cancer can have 25 to 50 copies of the ERBB2 gene, resulting in a 40- to-100-fold increase in ERBB2 receptor expression in comparison to normal cells, hence why ERBB2 is targeted by anti-ERBB2 antibodies and, more recently, immunotherapy [63,64]. Here, ERBB2 is linked to breast cancer.