Radioimmunotherapy with iodine(Drug information on iodine) I-131 tositumomab (Bexxar) produced tumor shrinkage in 97% of previously untreated patients with advanced-stage, low-grade non-Hodgkin’s lymphoma, according to a recent study at the University of Michigan Comprehensive Cancer Center. Most notably, 76% of patients achieved a complete remission, with no sign of cancer. In addition, 84% of the 34 patients who, at the start of the trial, showed evidence of lymphoma at the molecular level achieved molecular remission for as long as 3 years.
These promising results from the first completed study of a first-line, stand-alone radioimmunotherapy for cancer were presented at the recent meeting of the American Society of Clinical Oncology (ASCO) by Mark S. Kaminski, md, University of Michigan’s professor of hematology/oncology and codirector of its leukemia/lymphoma and bone marrow transplant programs. Dr. Kaminski also conducted the original studies in the therapeutic development of tositumomab.
Remissions Beyond 3 Years
“We are extremely excited by these findings, which showed remarkable response rates and molecular remissions ongoing beyond 3 years,” said Dr. Kaminski. “Molecular remissions are seldom seen with chemotherapy in low-grade lymphoma and appear to coincide with prolonged, durable responses. Furthermore, these results demonstrate the potential of this treatment as an effective and well-tolerated first-line, single-agent treatment for low-grade lymphoma, a disease without a known cure.”
The phase II study enrolled 76 patients with previously untreated, advanced-stage, low-grade follicular lymphoma. Patients received a trace dose of the radiolabeled tositumomab, followed 1 to 2 weeks later with a therapeutic dose. In contrast to common chemotherapy regimens, no further treatment was given.
Tositumomab was well tolerated. Moderate, reversible low blood counts were seen, but no patients required hematologic supportive care. Human antimouse antibodies were developed by 62% of the patients, about two-thirds of whom experienced flu-like symptoms lasting less than 1 week.
Most Patients Responded
Virtually all patients (74/76) responded in some way to treatment. An impressive number of patients (58) achieved a complete response. The investigators project that about 70% of those patients will continue to be disease-free for at least 3 years.
In addition, all patients were tested for detectable signs of disease in bone marrow before and after therapy. Of the 37 patients who had molecular signs of the cancer before treatment, 31 achieved molecular remissions when measured again later. About 75% of those 31 patients are projected to remain in remission for at least 3 years.
Molecular remissions were determined by a rigorous use of polymerase chain reaction technology, arguably the most sensitive cancer detection method available today. Traditionally, a remission is measured by a patient’s disease-free status based on the absence of symptoms through examination and medical imaging, whereas molecular remissions are based on tests at the DNA level to see if the disease has been eradicated.
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