Results showed that HER2/ECD levels at diagnosis were more elevated in advanced breast cancer that HER2/ECD is not a substitute for HER2 status determination, that circulating HER2/ECD levels at diagnosis are significantly correlated with clinical outcome, and that HER2/ECD can be useful in monitoring the efficacy of trastuzumab neoadjuvant treatment and in assisting the early detection of relapse. This evidence concerns the gene ERBB2 and breast carcinoma.