Outcomes Research in Review

Combination of Ibrutinib and Rituximab Prolongs Progression-Free Survival in Waldenström Macroglobulinemia

Dimopoulos MA, Tedeschi A, Trotman J, et. al. Phase 3 trial of ibrutinib plus rituximab in Waldenström’s macroglobulinemia. N Engl J Med. 2018;378:2399-2410.



Study Overview

Objective. To evaluate the efficacy of the combination of ibrutinib plus rituximab in patients with previously untreated or recurrent and rituximab-sensitive Waldenström macroglobulinemia.

Design. International, randomized phase 3 trial.

Setting and participants. Patients from 45 sites in 9 countries were enrolled after receiving a centrally confirmed diagnosis of Waldenström macroglobulinemia that required treatment according to current guidelines.1 Patients who were treatment-naive or had relapsed disease were eligible. Those with relapsed disease must have demonstrated response to rituximab in the past with a duration of response of at least 12 months. Patients who were rituximab resistant or those who received rituximab within the prior 12 months were excluded.

Intervention. Patients were randomized in a 1:1 fashion to receive oral ibrutinib 420 mg once daily or placebo. All patients received rituximab 375 mg/m2 at weeks 1 to 4 and 17 to 20. Treatment was continued until disease progression or intolerable adverse effects developed. Patients were stratified according to International Prognostic Scoring System for Waldenström Macroglobulinemia (IPSS) score, number of prior therapies, and performance status. Those who received placebo were permitted to crossover to receive ibrutinib at the time of progression.

Main outcome measures. The primary outcome of this study was progression-free survival (PFS). Secondary endpoints included time to next treatment, overall survival (OS), response rate, sustained hematologic improvement, quality of life, and safety. MYD88 and CXCR4 mutational status were assessed on pre-treatment bone marrow specimens.

Results. 150 patients were randomized to receive ibrutinib-rituximab (75 patients) or placebo-rituximab (75 patients). The median age was 69 years, and approximately one-third of patients were over the age of 75 years; 45% were treatment-naive. Those with relapsed disease had received a median of 2 prior treatments, and 85% of these received prior rituximab. Baseline characteristics were well balanced between the 2 groups. Mutation data was available for 136 patients enrolled, and MYD88 L265P and CXCR4 WHIM mutations were found in 85% and 36%, respectively. Rituximab therapy was completed in 93% of patients in the ibrutinib group and 71% in the placebo group.

30-Month PFS Rates by Mutational Status

After a median follow up of 26.5 months, the 30-month PFS was 82% in the ibrutinib group and 28% in the placebo group (median not reached vs. 20.3 months; hazard ratio 0.20, 95% confidence interval [CI] 0.11-0.38). This translated into an 80% reduction in the risk of progression or death. Overall, there was a low rate of histologic transformation to diffuse large B-cell lymphoma in the study group (2 patients in ibrutinib arm and none in placebo arm). In the treatment-naive subgroup, at 24 months the PFS rate was 84% in the ibrutinib arm compared with 59% in the placebo arm. In those with recurrent disease, the 30-month PFS was 80% in the ibrutinib arm compared with 22% in the placebo arm. Analysis across different MYD88 and CXCR4 genotypes showed consistent rates of higher PFS with ibrutinib-rituximab (Table). In addition, 30-month PFS was higher with ibrutinib regardless of IPSS score.

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