ERBB2 and breast cancer: Trastuzumab, an FDA-approved mAb for targeting HER2/neu in breast cancer malignancies, has been labeled with [225Ac]Ac, and its in vitro cytotoxicity was investigated against breast cancer spheroids MCF7, MDA-MB-361 (MDA), and BT-474 (BT) as a potential agent for RIT [157].