Approximately 90 patients will be randomized in a 2:1 (q4 : q2) ratio to one of two treatment arms at up to 26 study centers worldwide. Patients will continue to receive the same total 4-week dose that they were receiving prior to study enrollment, however, they will be randomized to receive either their total 4-week dose in two infusions, one infusion every 2 weeks or their total 4-week dose in one infusion every 4 weeks. The randomization scheme will ensure a 2:1 balance between the every 4-week versus every 2-week infusion groups, respectively.