Study shows radioactive antibodies produce durable remissions of three years or more
NEW ORLEANS - A radioactive antibody compound known as Bexxar produced tumor shrinkage in 97 percent of 76 previously untreated patients with advanced-stage, low-grade non-Hodgkins lymphoma (NHL) in a new study at the University of Michigan Comprehensive Cancer Center.
Most notably, 76 percent of patients achieved a complete remission, with no sign of cancer. In addition, 84 percent of patients with evidence of lymphoma at the molecular level at the start of the trial achieved molecular remission for as long as three years with the treatment. Molecular remissions were determined by a rigorous use of polymerase chain reaction, or PCR, technology, arguably the most sensitive cancer detection method available today.
These promising results, from the first completed study of a first-line, stand-alone radioimmunotherapy for cancer, were presented today at the meeting of the American Society of Clinical Oncology by Mark S. Kaminski, M.D., U-M professor of hematology/oncology and co-director of the U-M's leukemia/lymphoma and bone marrow transplant programs.
The original studies in the therapeutic development of Bexxar, or Iodine I 131 tositumomab, were done at the U-M by Kaminski and his colleague Richard Wahl, M.D., professor of nuclear medicine and radiology. The therapy is now being jointly developed by Coulter Pharmaceutical, Inc. and SmithKline Beecham.
"We are extremely excited by these findings, which showed remarkable response rates and molecular remissions lasting up to and beyond three years," says 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."
Bexxar is a radioimmunotherapy that combines a mouse monoclonal antibody attached to radioactive iodine 131. It attaches to a protein found only on the surface of the blood's B-cells, including those turned malignant in non-Hodgkin's lymphoma patients. The compound is believed to work through a combination of immune system activity involving the monoclonal antibody, and effects from the radiation released by the iodine 131. Through this targeted approach, the tumor cells receive a greater concentration of therapeutic radiation while minimizing radiation exposure to normal tissues.
The Phase II study, conducted entirely at the U-M, enrolled 76 patients with previously untreated, advanced-stage, low-grade follicular lymphoma. The study was designed to evaluate the safety and efficacy of Bexxar as an NHL treatment given by itself and as the first treatment approach.
Patients received a trace dose, followed one to two weeks later with a therapeutic dose. No further treatment was given. This is in contrast with what patients would have experienced if given chemotherapy treatment, which is commonly repeated every three to four weeks for several months.
Patients tolerated Bexxar treatment well. Moderate, reversible low blood counts were seen, but no patients required hematologic supportive care. Sixty-two percent of patients developed human anti-mouse antibodies (HAMA). About two thirds of these patients experienced flu-like symptoms lasting less than one week.
Virtually all patients - 74 of 76 - responded in some way to treatment. An impressive number of patients (58) achieved a complete response. About 70 percent of those patients are projected to continue to be disease-free for at least three years.
PCR analyses were conducted to test for detectable signs of disease in bone marrow among all patients 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 percent of such patients are projected to avoid relapse o f their disease for at least three years.
A remission usually measures a patient's disease-free status based on the absence of disease signs in examination and medical imaging. But molecular remissions are based on tests at the DNA level to see if the disease has been eradicated. The PCR assay can detect one cancerous cell among a million normal cells; in non-Hodgkin's lymphoma the test looks for aberrant cells in the bone marrow and blood and can demonstrate how completely the disease has been destroyed by treatment.
Non-Hodgkin's lymphoma is a form of cancer that affects the blood and lymphatic tissues. The sixth leading cause of cancer death in the U.S., NHL also has the second fastest-growing incidence rate of all cancers.
According to the National Cancer Institute, nearly 300,000 Americans have NHL, among them 140,000 with the low-grade or transformed low-grade forms of the disease. In more than 30 years, the survival rates of low-grade NHL patients have not changed, and patients continue to die from the disease or complications associated with current treatments.