U3-1402/patritumab-GGFG-DXd is the first HER3-targeting antibody-drug conjugate (ADC) showing clinical efficacy in non-small-cell lung cancer. However, an elevated proportion of patients with this cancer express low levels of HER3 and are nonresponsive to this ADC. In addition, novel ADCs are needed to treat other cancer types, including colorectal cancer.