A phase 2 expanded access study of zanubrutinib (ZANU) in patients (pts) with Waldenstr_om Macroglobulinemia (WM).

e19522 Background: Bruton tyrosine kinase (BTK) inhibition is an emerging standard of care for WM. The next-generation BTK inhibitor ZANU (BGB-3111), designed to maximize BTK occupancy and minimize off-target inhibition of other kinases, is approved by the United States (US) Food and Drug Administration, Health Canada, and the European Union at a dose of 320 mg once daily (QD) or 160 mg twice daily (BID) for adult pts with WM. BGB-3111-216 is a single-arm expanded access study of ZANU in treatment-naïve (TN) pts who were unsuitable for standard chemoimmunotherapy or pts with relapsed refractory (R/R) WM. This study provides real-world experience with ZANU in pts with WM. Methods: Eligible pts with TN or R/R WM received ZANU 320 mg QD or 160 mg BID orally. Primary endpoint was the number of pts enrolled/treated and enrolling sites. Secondary endpoints included treatment-emergent adverse events (TEAEs) of special interest, disease response rate, progression-free survival (PFS), and overall survival (OS). Response was evaluated by investigator assessment according to the 6th International Workshop on WM ( Br J Haematol. 2013;160(2):171-6) every 6 mo at minimum. The study was closed by the sponsor in July 2021 and active pts were transitioned to commercial ZANU via a patient assistance program. Results: Fifty pts with WM (17, TN; 33, R/R) were enrolled between December 2019 and June 2021 across 10 academic and community medical centers in the US. Median age was 72 years, 54% had intermediate-, 40% had high-risk disease, and the median number of prior therapies for R/R pts was 2. Median treatment exposure was 9.2 mo (range, 1.4-20.0). Thirty-eight (76%) pts had ≥1 TEAE, and 36 (72%) had ≥1 TEAE of special interest. Grade ≥3 TEAEs of special interest were hypertension (8%), infection (8%), atrial fibrillation/flutter (2%), neutropenia (2%), and second primary malignancy (2%). No new safety signals were observed. In pts with ≥1 response evaluation, 39% achieved a best overall response (BOR) of very good partial response. Overall response rate was 85.4% and major response rate was 73.2% (Table). Of the 4 pts with BOR of progressive disease, 3 had IgM values that met partial response criteria before the 6-mo response assessment. PFS and OS were immature due to short follow-up, and the median was not met. Conclusions: These real-world expanded access study results were consistent with the established ZANU profile in WM or other B-cell malignancies when administered as oral monotherapy at 160 mg BID or 320 mg QD in pts with intermediate or high-risk R/R or TN WM. Clinical trial information: NCT04052854. [Table: see text]