90Yttrium-ibritumomab tiuxetan appears to be effective in the treatment of patients refractory to treatment with rituximab, but response rates decrease with increasing tumor size. 90Y-ibritumomab tiuxetan was approved by the FDA in 2002 for the treatment of patients with relapsed or refractory low-grade, follicular, or CD20+ transformed B-cell non-Hodgkin's lymphoma (NHL), and rituximab-refractory follicular NHL.