ERBB2 and breast cancer: For example, in one of the largest prior studies, 1703 HER2-positive cases were divided based on HER2 FISH ratio levels or HER2 FISH CN levels and found no significant influence of the degree of HER2 amplification on disease-free survival after 1-year of adjuvant trastuzumab after a median 2-years of follow-up in early stage BC patients treated with prior adjuvant chemotherapy34.