CD20 has proven to be an excellent target for the treatment of
B-cell lymphoma, first for the chimeric
monoclonal antibody rituximab (
Rituxan), and more recently for the radiolabelled
antibodies Y-90
ibritumomab tiuxetan (
Zevalin) and I-131 tositumomab (
Bexxar).
Radiation therapy effects are due to beta emissions with path lengths of 1-5 mm; gamma radiation emitted by I-131 is the only radiation safety issue for either product. Dose-limiting toxicity for both radiolabelled
antibodies is reversible bone marrow suppression. They produce response rates of 70%-90% in low-grade and
follicular lymphoma and 40%-50% in transformed low-grade or
intermediate-grade lymphomas. Both products produce higher response rates than related unlabelled
antibodies, and both are highly active in patients who are relatively resistant to
rituximab-based
therapy. Median duration of response to a single course of treatment is about 1 year with complete remission rates that last 2 years or longer in about 25% of patients. Clinical trials suggest that anti- CD20
radioimmunotherapy is superior to total body irradiation in patients undergoing stem cell supported
therapy for
B-cell lymphoma, and that it is a safe and efficacious modality when used as consolidation
therapy following
chemotherapy. Among cytotoxic treatment options, current evidence suggests that one course of anti-CD20
radioimmunotherapy is as efficacious as six to eight cycles of
combination chemotherapy. A major question that persists is how effective these agents are in the setting of
rituximab- refractory
lymphoma. These products have been underutilised because of the complexity of treatment coordination and concerns regarding reimbursement.