To investigate whether HER2-trogocytosis prior to treatment could be used to predict HER2+ breast cancer patients’ responses to PST consisting of anthracyclin followed by taxan plus trastuzumab, we evaluated HER2 trogocytosis in formalin-fixed paraffin embedded tumor samples collected from patients at Kyoto University Hospital from 2008 to 2012 (N = 13; 7 pCR and 6 non-pCR patients were included). The gene discussed is ERBB2; the disease is neoplasm.