We also report the enhanced efficacy of DAN-311 in a HER2-low breast cancer (JIMT-1) xenograft mouse model….DAN-311 exhibited significantly greater tumor growth inhibition compared to vehicle, core particle, and trastuzumab….DAN-311, a Next-Generation ADC with a HER2-targeting agent (trastuzumab) on a polymeric nanoparticle conjugated with CPT demonstrated a significant ability to inhibit tumor growth in a HER2-low xenograft mouse model.