An antibody-drug conjugate (ADC) composed of a monoclonal antibody directed against the cell surface glycoprotein mesothelin and conjugated to an as of yet undisclosed cytotoxic drug, with potential antineoplastic activity. The monoclonal antibody moiety of anti-mesothelin ADC BMS-986148 targets and binds to the tumor-associated antigen mesothelin. Upon internalization, the cytotoxic agent kills or prevents cellular proliferation of mesothelin-expressing tumor cells through an as of yet undescribed mechanism of action. Mesothelin is overexpressed by all mesotheliomas and a variety of other cancers, while it is minimally expressed in normal tissue.