ERBB2 and neoplasm: Among prognosis-related immunohistochemical factors, including hormone receptors such as estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and Ki-67, ER-positive/HER2-negative, HER2-positive, and triple-negative, are three primary entities typically considered clinically based on immunohistochemical findings of the primary tumor biopsy specimen.