An antibody-drug conjugate (ADC) composed of an antibody against a structural homolog of the urokinase-type plasminogen activator receptor (uPAR) and tumor-associated antigen, C4.4a, and conjugated with a cytotoxic agent, with potential antineoplastic activity. Upon intravenous administration, lupartumab amadotin targets and binds to C4.4a-expressing tumor cells. Upon binding and cell entry, the cytotoxic agent kills the tumor cell. C4.4a, a glycolipid-anchored membrane protein and a member of the Ly-6 family, is overexpressed by a variety of cancer cell types whereas it is minimally expressed on healthy cells.