ROCKVILLE, MarylandFor the first time, the US Food and Drug Administration has approved the use of a radioisotope attached to a monoclonal antibody for the treatment of cancer.
The agency granted marketing approval to the radioimmunotherapy Zevalin (ibritumomab tiuxetan, IDEC Pharmaceuticals) in combination with Rituxan (rituximab) for use in treating patients with relapsed or refractory low-grade follicular or transformed B-cell non-Hodgkin’s lymphoma (NHL) who have failed to respond to standard chemotherapy or to treatment with Rituxan alone.
Both Zevalin and Rituxan are monoclonal antibodies that target normal and malignant B cells via the CD20 antigen and significantly reduce tumor size. The antibody in Zevalin, however, is bound to one of two radioisotopes: indium-111 or yttrium-90.
The novel combination regimen is administered in two parts. Patients first receive Rituxan, which is followed by a Zevalin treatment in which the monoclonal antibody is linked to a low-dose of indium-111. This Zevalin dose is used as a screening procedure.
Those patients whose tumors have been properly targeted by Zevalin go on to a second round of infusions 7 to 9 days later. A patient again receives Rituxan, followed by a different form of Zevalin in which the antibody is bound to yttrium-90, a more powerful radioisotope that can provide a treatment benefit.
"Zevalin represents a major advance in the treatment of certain non-Hodgkin’s lymphomas, especially among patients who have become refractory to other treatment options," said Thomas E. Witzig, MD, a hematologist at the Mayo Clinic, Rochester, Minnesota, and a leader in the clinical trials of the drug. "Unlike standard chemotherapy, which is given over as many as 4 months, Zevalin can be administered in an outpatient setting over 8 days with approximately 12 weeks of follow-up." According to IDEC, CD20-negative progenitor cells generally replenish normal B cells killed by Zevalin within 6 to 9 months.
The FDA granted Zevalin both full and accelerated approval, as recommended by the Oncologic Drugs Advisory Committee last September. The accelerated approval requires IDEC to conduct further studies to demonstrate the safety and efficacy of the drug in relapsed or refractory patients who have not yet received Rituxan.