"real-Life" Data of Zanubrutinib in Patients with Waldenström Macroglobulinemia: A Multicenter Retrospective Study

Introduction: Waldenström macroglobulinemia (WM) is a rare indolent lymphoma. Zanubrutinib (ZAN), a second-generation BTK inhibitor, has been approved for the treatment of WM in any line of therapy in 2021. Between November 2020 and January 2022, an expanded access program of ZAN opened in Israel for the treatment of patients with relapsed/refractory (R/R)-WM or those ineligible for chemotherapy or ibrutinib in first line. Methods: This is a multicenter retrospective study aiming to provide real-world data on ZAN in patients with WM in Israel. Demographic and clinical data were collected and coded from electronic files. Response was evaluated by the investigator's assessment. As the program closed, patients transitioned to commercial ZAN. Results: Thirteen patients (12 R/R; 1 treatment-naive) were enrolled across 8 centers in Israel. The median age at ZAN initiation was 71 years (range, 50-85); 6 were males; 10 had high IPSS-WM. R/R patients had a median of 1 (1-4) prior lines of therapy. Other than progressive disease after chemoimmunotherapy, the most common considerations for choosing ZAN were patients' age and/or comorbidities (n = 5), as well as ibrutinib toxicity. The initial ZAN dose was reduced in 4 patients. The median time on ZAN was 19.5 months (2.9-29.5). Of 12 evaluable patients, the ORR was 83% with 3 minor responses, 6 PRs, and 1 VGPR. With a median follow-up of 19.6 months, 7 patients were still on ZAN, 5 progressed, 4 while on ZAN, and 1 after ZAN was stopped due to AE. Eighteen-month PFS and OS were 60.5% and 77%, respectively. Eight (61%) patients had AEs of any grade, and 3 (23%) of grade 3-4; 2 stopped ZAN due to congestive heart failure and extreme fatigue. Conclusion: The results of this real-world high-risk population are consistent with prospective studies highlighting the efficacy and safety of ZAN.