A new study published in the Journal of Clinical
Oncology (19:3918-3928, 2001) reported that radioimmunotherapy with tositumomab/iodine-131
tositumomab (Bexxar), produced more durable complete or partial clinical
responses in patients with low-grade and transformed low-grade non-Hodgkin’s
lymphoma (NHL) than did their last round of chemotherapy. All patients in the
study had chemotherapy-refractory NHL. Typically, response rates and durations
of response in refractory patients decline with each successive therapy, but in
this study, the tositumomab/iodine-131 tositumomab combination was shown to
reverse the expected outcome.
"Bexxar therapy has resulted in durable remissions in a low-grade NHL
population refractory to chemotherapy, and in those with transformed low-grade
NHLan aggressive form of lymphoma that is associated with a very poor
prognosis," said Mark S. Kaminski, md, professor of internal medicine and
codirector of the leukemia/lymphoma bone marrow transplant program at the
University of Michigan Cancer Center. "The results of this study
demonstrate a measurable improvement over previous therapy and suggest a
reversal of the downward trend seen in relapsed and refractory patients
following prior treatments."
Significantly Higher Response Rates
The study investigated the safety and efficacy of tositumomab/iodine-131
tositumomab compared to the patient’s previous chemotherapy. Researchers
observed a partial or complete response to the investigational combination in
65% of patients vs a 28% response rate to the patient’s last chemotherapy
agent. Results for patients achieving a complete response were 20% after
tositumomab/iodine-131 tositumomab compared to 3% after treatment with their
previous drug. For patients who achieved a complete response with tositumomab/iodine-131
tositumomab, the median duration of response has not yet been reached, and 9 of
the 12 patients with complete responses have ongoing responses ranging from 32.3
to 47.4 months.
"Bexxar demonstrated a high rate of response and a low rate of
hematologic toxicity in a heavily treated patient population," said Dr.
Tositumomab/iodine-131 tositumomab combines the targeting ability of a
monoclonal antibody and the therapeutic potential of radiation, with
patient-specific dosing. The radiolabeled monoclonal antibody attaches to the
target marker CD20 found on NHL cells, thereby eliciting an immune response and
delivering a dose of iodine-131 radiation to tumor cells.
"This targeted approach was designed to ensure that the tumor cells will
receive a greater concentration of the therapeutic radiation than normal
tissues, and the radioactive component is probably a major factor in the drug’s
antitumor effect," said Dr. Kaminski.