Triple-negative breast cancer (TNBC)—the most aggressive molecular subtype of breast cancer—is characterised by the absence of oestrogen receptor (ER) and progesterone receptor (PR) expression, as well as a lack of epidermal growth factor receptor 2 (ERBB2) gene amplification or ERBB2 protein overexpression [36]. The gene discussed is ERBB2; the disease is breast cancer.