A dual-targeted antibody-drug conjugate (ADC) consisting of a monoclonal antibody directed against the epidermal growth factor receptor (EGFR; HER1; ErbB1) and the epidermal growth factor receptor 3 (HER3; ErbB3) and conjugated to an as of yet not elucidated cytotoxic payload, with potential antineoplastic activity. Upon administration of anti-EGFR/anti-HER3 ADC BL-B01D1, the monoclonal antibody moieties simultaneously target and bind to EGFR and HER3 expressed on cancer cells. Following receptor internalization, the cytotoxic moiety is released and kills EGFR/HER3-expressing tumor cells through an as of yet unknown mechanism of action (MoA). EGFR and HER3, both upregulated and/or mutated in a variety of tumor cell types, play key roles in tumor cell proliferation. Simultaneously targeting both EGFR and HER3 may enhance the anti-tumor activity of BL-B01D1.