SAN FRANCISCO – Ofatumumab maintenance therapy nearly doubled progression-free survival in patients with relapsed CLL, according to a preplanned interim analysis of the phase III PROLONG study.
At a median follow-up of 19.1 months, progression-free survival was 15.2 months with the standard approach of observation alone and 29.4 months with maintenance ofatumumab (Hazard ratio, 0.50; P < .0001).
Ofatumumab (Arzerra) also significantly increased the median time to next treatment from 31.1 months to 38 months (HR, 0.66; P = .0108), Dr. Marinus van Oers reported at the annual meeting of the American Society of Hematology.
The benefit in progression-free survival (PFS) with maintenance was “statistically significant and clinical relevant” and was present in all subgroups, he said. It was independent of age, gender, number and type of prior treatment, minimal residual disease status at study entry, and “response at study entry, although we have the impression that it’s more effective in patients on PR [partial response] than in patients on CR [complete response],” he added.
The rationale for the trial lies in the fact that despite recent advances, there is still no curative treatment for chronic lymphocytic leukemia (CLL). Ofatumumab, a type 1 CD20 monoclonal antibody, has a role as maintenance in follicular lymphoma (FL), which shares similarities in biological behavior with CLL. This role is debated, but a recent meta-analysis shows ofatumumab maintenance prolongs PFS and tends to prolong overall survival in relapsed patients with FL, Dr. van Oers of the Academic Medical Center in Amsterdam, The Netherlands, observed.
PROLONG randomized 474 patients with relapsed CLL to observation or ofatumumab 300 mg in week 1 and 1,000 mg in week 2, and every 8 weeks for 2 years. All patients were in second or third remission and within 3 months of response assessment after the last reinduction treatment. Patients with refractory disease or prior maintenance therapy or stem cell transplantation were excluded.
At baseline, the median age was about 65 years, 70% had at least two prior treatments, 80% were in partial remission from their last CLL treatment, and less than 10% had poor-risk cytogenetics 11p or 17p deletions. At the time of the analysis, 25% of patients had received all 13 cycles of ofatumumab.
Adverse events of any grade were increased with the addition of ofatumumab versus placebo (86% vs. 72%; P < .0001). Sixty percent were related to study treatment, but none resulted in study withdrawal, Dr. van Oers said. In all, 17 patients on the experimental arm dropped out due to physician decision or patient wish.
Among grade 3 events, neutropenia was significantly increased with maintenance therapy versus placebo (24% vs. 10%; P < .0001) and there was a non-significant increase in infections (13% vs. 8%). Five deaths occurred in the observation arm and two in the ofatumumab arm, one due to sepsis two months after the end of treatment and the other due to unrelated GI obstruction.
Median overall survival has not been reached for either arm (HR, 0.85; P = .487), he reported on behalf of HOVON and the NORDIC CLL group, co-developers of the study.