Biological and clinical perspectives of cancer imaging and therapy with radiolabeled antibodies.

Cancer and other diseases that elaborate increased quantities of antigenic substances can be targeted with suitable antibodies labeled with radionuclides. Factors influencing this targeting include the nature, pharmacology, and physiology of the antibodies, the composition and physiology of the tissue targets, the character and linkage of the radionuclide to the antibody, the choice of radionuclide, and the method of administration of the radioimmunoconjugate. The current state of cancer imaging with gamma-emitting radiolabeled antibodies, using the more optimal Fab' antibody fragments conjugated with 99mTc and imaging by single-photon emission computed tomography, permits high detection rates (90% range) of tumors at or below 0.5 cm, thus disclosing lesions missed by conventional radiographic methods. In radioimmunotherapy, severe limitations are due to low antibody accretion in tumors (resulting in low target rad doses), inadequate conjugation of radiometals to antibodies, high red marrow toxicity, and human anti-antibody responses when foreign immunoglobulins are administered. However, radiosensitive tumors, such as lymphomas, have shown impressive clinical responses.