Disclosed is a method for measuring the effectiveness of therapy intended to kill malignant cells in vivo in a mammal, comprising the steps of obtaining monoclonal antibody that is specific to an internal cellular component of the mammal but not to external cellular components, wherein the monoclonal antibody is labeled; contacting the labeled antibody with tissue of a mammal that has received therapy to kill malignant cells in vivo, and determining the effectiveness of the therapy by measuring the binding of the labeled antibody to the internal cellular component. The internal cellular component is preferably insoluble intracellular antigen, and the label is preferably a radionuclide, a radiopaque material, or a magnetic resonance-enhancing material. Also disclosed is a method whereby the antibody to insoluble intracellular antigen is conjugated to an antineoplastic agent, so that upon administration of the antibody-antineoplastic agent conjugate, antineoplastic agent may be delivered to the tumor. Also disclosed are antibodies for use with the foregoing methods.