We confirmed that no TDM1R and TDXdR HER2+ BC cell lines showed growth inhibition when treated with 2 μg/mL of T-DM1 or T-DXd while parent BC cell lines showed over 90% cell death with the same treatment (Fig. 2B; TDM1R and TDXdR indicate resistance to TDM1 and T-DXd, respectively). Here, ERBB2 is linked to breast cancer.