An antibody-drug conjugate (ADC) composed of a monoclonal antibody directed against the T-cell checkpoint ligand B7-H4 (V-set domain-containing T-cell activation inhibitor 1; VTCN1; B7x; B7S1) linked to an as of yet unknown cytotoxic agent, with potential antineoplastic activity. Upon administration of anti-B7-H4 ADC BG-C9074, the anti-B7-H4 monoclonal antibody moiety targets and binds to B7-H4 expressed on tumor cells. Upon binding and internalization, the cytotoxic agent exerts an as of yet unknown mechanism of action (MoA) causing apoptosis in B7-H4-expressing tumor cells. B7-H4, a member of the B7 family of immune modulators, is upregulated in a variety of tumor cell types and tumor-associated macrophages (TAMs). It negatively regulates T-cell immune responses.