CURRENT STATUS OF RADIOIMMUNOTHERAPY

Radioimmunotherapy with radiolabeled monoclonal antibodies is increasi ngly effective for hematopoietic tumors, with a number of investigator s reporting persistent major responses. Radioimmunotherapy for solid t umors has been more difficult and only an occasional major response ha s been reported and these have so far not been persistent. Toxicity is predominantly hematopoietic, with platelets being most sensitive to t he effects of radiation. Even at ultra-high doses (up to 28 mCi/kg of I-131), second organ toxicity has not been reached. Rational approache s to dose planning are becoming possible with improvements in dosimetr y, based on quantitative SPECT and PET imaging. Current therapeutic in dices for tumor/marrow, the most radiosensitive organ, are in the rang e of 5-10 to 1. This is probably still too low for curative treatment of solid tumors, and further refinements, perhaps based on novel antib ody formulations, are needed.