Breast cancer patients with primary tumor characteristics such as HR-negative status (basal-like cell type/triple-negative), high grade, high Ki-67 index, HER2 overexpression, molecular subtype (luminal B-like, HER2 positive, triple-negative) have a higher risk of developing BMBC [17,48,49,50,51]. The gene discussed is ERBB2; the disease is breast cancer.