ERBB2 and breast cancer: In summary, the use of HER2/CD3 BSABs in treating patients with BC has resulted in a DCR of 33%, along with promising early antitumor activity from BSABs targeting the HER2 domains ECD2 and ECD4 in patients with metastatic BC who had failed multiple prior treatments (DCRs of 54% and 76.8%) [131, 169].