Patients with Waldenström macroglobulinemia (WM) in the real world had clinical benefit from ibrutinib monotherapy, but they also had increased toxicity, reported a study in the British Journal of Haematology.
The study cohort included 80 patients with WM from the Mayo Clinic who were consecutively seen between September 1, 2018, and February 1, 2019, and treated with ibrutinib alone. Among the 80 patients, 67 were previously treated and 13 were treatment-naive.
The median follow-up was similar between the 2 subgroups (previously treated, 18 months vs treatment-naive, 19 months). For the study cohort, the median time on therapy was 12.5 months.
Among the patients with available response data (54 of 80 patients), an overall response rate (ORR) of 91% was seen, which included a 100% ORR for treatment-naive patients and 89% ORR for previously treated patients. The major response rate for the entire cohort and each subgroup was 78%. The progression-free survival at 18 months was 82%. The estimated median overall survival was 41 months.
Common nonhematological adverse events were fatigue (12%), atrial fibrillation (11%), and grade 2 or higher elevated liver enzymes (7%).
In all, 25 patients (31%) discontinued treatment with ibrutinib, most of whom (21 patients) had been previously treated. The most common reason for treatment discontinuation was disease progression (32%) followed by atrial fibrillation (16%) and elevated liver enzymes (12%).
Patients who discontinued treatment were evaluated for IgM rebound phenomenon, and of the 14 patients who were evaluable, 5 (36%) had IgM rebound.
“Ibrutinib therapy, outside of clinical trials, is effective in WM, but is associated with toxicities and challenges, including IgM rebound and a high drug discontinuation rate for reasons other than disease progression,” the study authors wrote.
Abeykoon JP, Zanwar S, Ansell SM, et al. Ibrutinib monotherapy outside of clinical trial setting in Waldenström macroglobulinaemia: practice patterns, toxicities and outcomes [published online August 29, 2019]. Br J Haematol. doi: 10.1111/bjh.16168