ERBB2 and breast cancer: In summary, for HER2 positive breast cancer, ERBB2 amplification alone is reported as a sensitivity biomarker for the treatment with trastuzumab, trastuzumab emtansine and other combination treatments in clinical guidelines, while in clinical and preclinical studies, combination of ERBB2 amplification with other biomarkers are being investigated in different experimental settings and with different drug combinations.