Results from the phase 3 PROLONG study demonstrated that maintenance therapy with ofatumumab was superior to observation in terms of progression-free survival in patients with relapsed chronic lymphocytic leukemia (CLL), according to an article published online in the Lancet Oncology.1

Ofatumumab is a human anti-CD20 monoclonal antibody with efficacy as monotherapy in refractory CLL. Investigators sought to determine the efficacy and safety of ofatumumab as maintenance treatment for patients in remission after re-induction treatment for relapsed CLL.

Investigators enrolled 474 patients: 238 patients were randomly assigned to receive ofatumumab maintenance treatment and 236 were randomly assigned to observation.

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With a median follow-up of 19.1 months, progression-free survival was 29.4 months in the ofatumumab group (95% CI: 26.2-34.2) compared with 15.2 months in the observation group (HR: 0.50; 95% CI: 0.38-0.66; P<0.0001).

In regard to safety, the most common grade 3 or higher adverse events up to 60 days after last treatment were neutropenia (24% in ofatumumab group; 10% in the observation group); infections (13% compared with 8%). Eight percent of patients in the ofatumumab group and 1% of patients in the observation group experienced adverse events that led to treatment discontinuation.

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Up to 60 days after final treatment, two deaths related to adverse events occurred in the ofatumumab group compared with five deaths in the observation group. None of the deaths were treatment-related.

Investigators concluded that these data are important for the development of optimum maintenance treatment strategies in patients with relapsed CLL.


  1. van Oers MHJ, Kuliczkowski K, Smolej L, et al. Ofatumumab maintenance versus observation in relapsed chronic lymphocytic leukaemia (PROLONG): an open-label, multicentre, randomised phase 3 study. [published online ahead of print September 13, 2015]. Lancet Oncol. doi: 10.1016/S1470-2045(15)00143-6.