We also evaluated these ADCs for in vitro cytotoxicity using HER2 positive- (KPL-4, JIMT-1, BT-474, and SKBR-3) and negative (MDA-MB-231) breast cancer cell lines (Fig. 3c–e, Supplementary Fig. 11, and Supplementary Tables 3, 4). This evidence concerns the gene ERBB2 and breast cancer.