Radioimmunotherapy for B-cell non-Hodgkin lymphoma.

Radioimmunotherapy (RIT) combines the targeting advantage of a monoclonal antibody with the radiosensitivity of non-Hodgkin lymphoma (NHL) cells. There are now two radioimmunoconjugates (RICs) - ibritumomab tiuxetan (Zevalin) and tositumomab (Bexxar) - that are approved by the FDA in the US for relapsed low-grade or follicular B-cell NHL. Both agents target the CD20 antigen on B-cell lymphoma cells. In relapsed disease, single doses of RIT produce an 80% overall response rate, with approximately 20% of patients achieving durable responses. RIT is very well tolerated and is delivered on an outpatient basis over 1 week. The only significant toxicity is reversible myelosuppression. Both RIT agents have demonstrated high anti-tumor activity in patients who are refractory to rituximab. Current trials are testing RIT as initial therapy with rituximab maintenance, as adjuvant therapy after chemotherapy, or in high-dose protocols with stem-cell support.