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Radiolabeled MoAb Allows Higher RT Doses

Radiolabeled MoAb Allows Higher RT Doses

LOS ANGELES--Use of a radiolabeled monoclonal antibody in patients with relapsed B-cell lymphoma may allow higher doses of radiation to the tumor and less toxicity to normal organs, Oliver W. Press, MD, PhD, of the University of Washington Medical Center, Seattle, said in his ASCO presentation.

In this NCI-funded phase II trial, the CD20 antibody, known as B1 (supplied by Coulter Corporation, Miami), was conjugated to high doses of iodine 131 (345 to 787 millicuries). After a therapeutic dose given by injection, patients received either peripheral blood stem cell or bone marrow support.

Of 25 patients enrolled in the study, all with B-cell lymphoma expressing CD20 that had relapsed after at least one round of conventional chemotherapy, 22 exhibited favorable localization of the radiation to tumor sites after a test dose, and 21 received a therapeutic dose.

Seventeen patients had a complete response, and 16 have remained progression free for up to 3 years. At a median follow-up of 1 year, overall survival is 93% and progression-free survival is 62%.

All patients had severe neutropenia and thrombopenia; there was one fatal infection and one serious case of cardiopulmonary toxicity. "Nevertheless, short-term toxicity was less than we have experienced in Seattle with our conventional transplant regimens," he said.

Dr. Press concluded that the radiolabeled antibody when given at the maximum tolerated dose produces a high response rate with many responses of long duration, but stressed that further follow-up is needed to determine response durability and long-term toxicity.

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