ERBB2 and breast cancer: While the HER2xAPLP2 bsAb increased HER2 internalization and lysosomal trafficking versus trastuzumab, HER2xAPLP2 bsADC efficacy was inferior to a bivalent HER2 ADC in BC xenograft models, suggesting that HER2 bivalent engagement may be a more effective strategy for improved ADC efficacy.