An antibody-drug conjugate (ADC) composed of an antibody targeting the tumor-associated antigens (TAAs) human prostate-specific membrane antigen (PSMA) and six transmembrane epithelial antigen of the prostate 1 (STEAP1), linked to an as of yet undisclosed cytotoxic payload, with potential antineoplastic activity. Upon administration of anti-PSMA/STEAP1 ADC ABBV-969, the antibody moiety targets and binds to PSMA and STEAP1 expressed on tumor cells. Following receptor internalization, the cytotoxic payload is released and induces tumor cell death through an as of yet unknown mechanism of action. PSMA is expressed on the membrane of prostatic epithelial cells and overexpressed on prostate tumor cells as well as a variety of other solid tumors. STEAP1 is overexpressed in a variety of cancers including prostate cancer.