Table 2 lists some miRNA biomarkers associated with breast cancer molecular subtypes. This classification allows us to stratify breast cancers according to their molecular subtype, which guides the diagnosis and treatment decisions and predicts prognosis. As far as the treatment of breast cancer is concerned, two main targeted therapies are commonly used: hormone therapy for hormone receptor-positive tumors [105] and anti-HER2 therapy for HER2+ tumors [106]. The gene discussed is ERBB2; the disease is breast cancer.