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I-131 Tositumomab More Effective Than Unlabeled Antibody in Relapsed or Refractory NHL

I-131 Tositumomab More Effective Than Unlabeled Antibody in Relapsed or Refractory NHL

ANN ARBOR, Michigan—Tositumomab with radioactive I-131 attached (Bexxar)
is more effective than the unlabeled antibody in relapsed or refractory
CD20-positive non-Hodgkin’s lymphoma (NHL), according to Mark S. Kaminski,
MD. Dr. Kaminski reported data from a randomized, open-label, multicenter
study comparing the two formulations at the 43rd Annual Meeting of the
American Society of Hematology. He is professor of internal medicine at the
University of Michigan Comprehensive Cancer Center in Ann Arbor.

Phase II Study

This phase II study was undertaken because evidence of efficacy seen in
clinical trials of unlabeled anti-CD20 antibodies raised questions about
whether the radioactive label might add toxicity without additional benefit.
Lymphoma regression had also been observed after imaging doses of
radiolabeled tositumomab. "Since the radiation provided by the imaging
dose is unlikely to provide a therapeutic effect, a clinical trial was
performed to determine the relative contribution of the radioisotope and
antibody to both the efficacy and toxicity of I-131 tositumomab
therapy," Dr. Kaminski said.

This report included data for 78 patients with a median follow-up of 25
months. Patients were randomized either to tositumomab and I-131 tositumomab
(arm A) or to unlabeled tositumomab (arm B). The patients in this study had
a median of two prior chemotherapies and had disease that progressed within
12 months of their last chemotherapy. Patients randomized to unlabeled
tositumomab (arm B) could cross over and receive treatment with the hot
antibody once their disease had progressed.

Median age was 55 years (range: 28-85), 58% of patients were males, 88%
were stage III/IV, 40% had elevated lactate dehydrogenase, and 41% had a
lymph node larger than 5 cm. The original NHL was follicular in 97% of
patients, and 17% had experienced transformation to an aggressive histology.

Radioiodide Component Provides Benefit

The results show that the radiolabeled antibody is clearly more effective
and produced significantly greater overall response rate, confirmed
responses, confirmed complete responses (CR), and time to progression (see
Table 1). "The median duration of confirmed responses for the
tositumomab/I-131 tositumomab-treated patients has not been reached, and
for the tositumomab treated patients it was 18 months," Dr. Kaminski
said.

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