Bortezomib-based therapy is effective and well tolerated in frontline and multiply pre-treated Waldenström macroglobulinaemia including BTKi failures: A real-world analysis.

Waldenström macroglobulinemia (WM) is a rare, incurable low grade lymphoma following a relapsing trajectory. Management strategies have evolved with the introduction of targeted therapy including new classes of Bruton tyrosine kinase inhibitor (BTKi). Treatment may however be limited particularly at relapse by a lack of drug availability and tolerability. We assessed the real-world efficacy and tolerability of bortezomib-containing regimens in patients with WM at frontline and relapse including those with prior BTKi resistance. Forty-one patients were identified with 44 bortezomib-containing regimens administered (n = 12 frontline, n = 32 relapse). Of patients treated at relapse, the median prior lines of therapy was 3 (range 1-7). 24% (10/41) of the cohort were refractory or intolerant to BTKi prior to bortezomib delivery. The median follow-up after bortezomib administration was 34 months (range 0-131). Overall response rate was 88%; 2-year overall survival and progression-free survival were 90% (95% confidence interval [CI] 73-96) and 76% (95% CI 55-87), respectively. Median time-to-next-treatment was 66 months. Neuropathy (grade 1-2) occurred in 24% (8/34) and did not result in treatment cessation in any case. Gastrointestinal disturbance occurred in 7% (3/41). Treatment discontinuations were rare (1/44; 2%), suggesting a manageable safety profile. Major response rate was comparable in those with prior BTKi compared with those without (75% [6/8] vs 84% [27/32], p = 0.61). Bortezomib should be considered as a treatment modality particularly in those who are refractory to BTKi.