Ofatumumab is active in patients with fludarabine-refractory CLL irrespective of prior rituximab: Results from the phase 2 international study

Ofatumumab, the human CD20 monoclonal antibody that binds a distinct epitope from rituximab, has demonstrated clinical benefit as monotherapy for patients with chronic lymphocytic leukemia refractory to fludarabine and alemtuzumab (FAref) and patients refractory to fludarabine with bulky (> 5 cm) lymph nodes (BF-ref). To potentially gain insight into outcomes in patients previously treated with or refractory to rituximab, we performed an ad hoc retrospective analysis in the final 96 FA-ref and 111 BF-ref patients. There were 117 patients previously treated with rituximab (98 rituximab-refractory); 89 patients were rituximab-naive. For rituximab-treated, rituximab-refractory, and rituximab-naive patients, overall response rate was 43%, 44%, and 53%; median progression-free survival was 5.3, 5.5, and 5.6 months; and median overall survival was 15.5, 15.5, and 20.2 months. There were no significant differences in ofatumumab-related infusion reactions, or hematologic or infectious adverse events between subgroups. In summary, ofatumumab monotherapy was effective and well tolerated in patients with fludarabine-refractory chronic lymphocytic leukemia, including in patients with previous rituximab exposure. This trial was registered at www.clinicaltrials.gov as #NCT00349349.