In an interim analysis of the phase III PROLONG trial reported in The Lancet Oncology, van Oers et al found that maintenance therapy with ofatumumab (Arzerra) prolonged progression-free survival vs observation in patients with chronic lymphocytic leukemia in complete or partial remission after second- or third-line treatment.
In this open-label trial, 474 adult patients from 130 sites in 24 countries were randomly assigned between May 2010 and June 2014 to receive ofatumumab maintenance at 300 mg followed by 1,000 mg 1 week later and every 8 weeks for up to 2 years (n = 238) or observation (n = 236).
Patients had not previously received maintenance treatment or autologous or allogeneic stem cell transplantation. The primary endpoint was investigator-assessed progression-free survival in the intent-to-treat population; the current report was from a prespecified interim analysis after occurrence of two-thirds of the planned study events.
Median follow-up was 19.1 months. Median progression-free survival was 29.4 months (95% confidence interval [CI] = 26.2–34.2 months) in the ofatumumab group vs 15.2 months (95% CI = 11.8–18.8 months) in the observation group (hazard ratio [HR] = 0.50, P < .0001). Median progression-free survival on independent assessment was 30.4 vs 14.8 months (HR = 0.55, P < .0001). Ofatumumab patients had longer time to next treatment (median 38.0 vs 31.1 months, HR = 0.66, P = .011). There was no difference between groups in progression-free survival after next treatment (HR = 1.00, P = .9977).
The most common grade ≥ 3 adverse events in the ofatumumab group were neutropenia (24% vs 10%) and infections (13% vs 8%). Adverse events led to discontinuation of treatment in 8% vs 1%. Adverse events led to death up to 60 days after the last treatment in two patients in the ofatumumab group and five patients in the observation group, with no deaths considered related to study treatment.
The investigators concluded: “Our data indicate that ofatumumab maintenance treatment improved both progression-free survival and time to next treatment in patients with relapsed chronic lymphocytic leukaemia who are in partial or complete remission after re-induction treatment….These data are important for the development of optimum maintenance strategies in patients with relapsed chronic lymphocytic leukaemia, notably in the present era of targeted drugs, many of which are to be used until progression.”
Marinus H. J. van Oers, MD, of Academic Medical Center, Amsterdam, is the corresponding author of The Lancet Oncology article.
The study was funded by GlaxoSmithKline and Genmab. For full disclosures of the study authors, visit www.thelancet.com/journals/lanonc.
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