ERBB2 and breast cancer: The prognosis of patients with stage IV breast cancer can be different depending on the molecular subtype of the disease (hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status), site(s) of metastasis, the number of sites involved in metastasis, the status of the lymph nodes, the previous treatment received, and the pathological and clinical characteristics of the disease (10, 11).