SAN FRANCISCO—Ofatumumab maintenance provided statistically significant and clinically meaningful benefits for patients with relapsed chronic lymphocytic leukemia (CLL) compared with observation, results from an interim analysis of the PROLONG open-label randomized study (Abstract 21) reported at the 56th American Society of Hematology (ASH) Annual Meeting and Exposition.

The results included improvement in progression-free survival (PFS) and a significantly prolonged time to next treatment, said Marinus H.J. van Oers, of the Academisch Medisch Centrum and HOVON in Amsterdam, the Netherlands.

Although there is still no curative treatment for CLL, with decreasing response duration with subsequent lines of therapy, there is interest in a safe and effective maintenance treatment, Dr. van Oers said when explaining the rationale for the study.

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Patients with complete or partial responses after second- or third-line treatment for CLL were randomly assigned 1:1 to receive ofatumumab 300 mg followed 1 week later by 1,000 mg every 8 weeks for up to 2 years (n=238) or observation (n=236). Follow-up was every 3 months for 5 years.

At the time of the interim analysis, 25% of patients had completed all 13 cycles of ofatumumab.

At a median follow-up of 19.1 months, median PFS (the study’s primary endpoint) was 29.4 months (95% confidence interval [CI] 26.2-34.2) for ofatumumab and 15.2 months (95% CI 11.8-18.8) for observation (hazard ratio [HR] 0.50; P<0.0001). Time to start of next therapy was significantly longer in the ofatumumab arm compared with observation (median of 38.0 versus 31.1 months [HR 0.66; P=0.0108], respectively).

Subgroup PFS analysis showed that compared with observation, hazard ratios favored treatment with ofatumumab regardless of patient characteristic (age, gender, response at study entry, number or type of prior therapies, or Binet stage) or baseline prognostic factor (minimal residual disease status, cytogenetics).

Ofatumumab was well-tolerated, with no unexpected toxicities. The most common grade 3/4 adverse event was neutropenia (24% in the ofatumumab arm versus 10% in the observation arm). Infections occurred in 13% of patients in the ofatumumab arm and 8% in the observation arm.

The study was conducted by the Haemato Oncology Foundation for Adults in the Netherlands (HOVON), the Nordic CLL Group, and GlaxoSmithKline.


  1. van Oers, Marinus HJ, et al. “21 Ofatumumab (OFA) Maintenance Prolongs PFS in Relapsed CLL: Prolong Study Interim Analysis Results.” ASH 2014. Oral Presentation. December 6, 2014.