Abstract
Introduction: The BTK inhibitor ibrutinib (IB) is highly active in WM, achieving major responses (CR+VGPR+PR) in approximately 70% of pts. However, VGPR is infrequent, with rates ≤15% in reported series (Treon NEJM 2015, Dimopoulos EHA 2016). BGB-3111 is a potent, highly-specific and irreversible BTK inhibitor, with greater selectivity than IB for BTK vs. other TEC- and HER-family kinases, and superior bioavailability. We previously reported that the recommended phase 2 dose of BGB-3111 is 320mg daily (in single or split dose) in pts with advanced B cell malignancies. This achieves plasma levels equivalent to 6-10 fold that of IB, and >90% continuous inhibition of BTK in lymph node biopsies. We specifically investigated the safety and efficacy of BGB-3111 in pts with WM in an expansion cohort of the initial Phase 1 trial. Reported here are updated results of this study, including data from WM specific expansion cohorts.
Aims: To define the safety profile, and clinical activity of BGB-3111 in pts with WM.
Methods: These results are from a pre-specified a component of a Phase 1 study (Part 1: dose escalation [DEsc] in pts with R/R B cell malignancies, Part 2: disease-specific dose expansion cohorts [EC] at the recommended Phase 2 dose that included patients with relapsed / refractory or previously untreated WM). Adverse events (AEs) were reported per CTCAE v4.03. Responses were determined according to the modified Sixth International Workshop on WM (IWWM) criteria. The data cut-off is 10 June 2016.
Results: As of 10 June 2016, 31 pts with WM have been enrolled; 6 pts in DEsc (40mg [n=2], 80mg [n=2], 160mg QD [n=1], and 320mg QD [n=1]), and 25 in the WM EC (160mg BID [n=18], 320mg QD [n=7]). Three pts in DEsc were increased to 160mg QD after analysis of DEsc data, as allowed by protocol. Twenty-four pts are included in this analysis; 5 pts were excluded because of short (<60 day) follow-up for safety and efficacy, and 2 pts accrued at a single site were excluded because of insufficient documentation at baseline. Patient demographics, disease characteristics, and prior treatment history are summarized in Table 1. BGB-3111 was well tolerated with 71% reporting no drug related AE >Gr 1 severity within the first 12 weeks of therapy. The most frequent AEs (>20%) of any attribution (all Gr 1/2) were upper respiratory infection (25%), diarrhea (25%), and nausea (21%). There were 2 SAEs assessed as possibly related to BGB-3111 (Gr 2 atrial fibrillation, Gr 3 cryptococcal meningitis); in both cases, BGB-3111 was temporarily held but safely resumed. In total, 2 pts developed AF (one Gr 1, one Gr 2). No serious hemorrhage (≥Gr 3 or CNS hemorrhage of any grade) was reported. After a median follow-up of 7.6 months (2-21 months), the response rate was 92% (22/24). The major response rate was 83% (20/24), with VGPR (>90% reduction in IgM and reduction in extramedullary disease) in 33% (8/24) and PR (50-90% reduction in IgM and reduction in extramedullary disease) in 50% (12/24) pts. Pts with WM refractory to their last therapy were equally responsive: major response 77% [10/13], VGPR 31% [4/13], PR 46% [6/13]. Median time to initial response and major response were 29 days and 34 days, respectively. IgM decreased from a median of 29.9g/l at baseline to 3.0g/l; hemoglobin increased from a median of 10.1 g/dl at baseline to 13.5g/l. Two of 3 pts who had a dose increase after reaching a stable IgM plateau had further falls in IgM levels after dose escalation. Kinetics of IgM and hemoglobin response are presented in Figure 1. Lymphadenopathy was present in 8 pts at baseline; serial CT demonstrated reduction or resolution in all 8 pts (27%-100% reduction in SPD). Only one patient discontinued BGB-3111, due to exacerbation of pre-existing bronchiectasis while in VGPR. There have been no cases of disease progression. Analysis of response by genomic characteristics (including MYD88 and CXCR4 mutational status) is ongoing.
Conclusions: BGB-3111 is well-tolerated and highly active in WM. The depth and quality of responses, as reflected by the VGPR rate of 33%, warrant a randomized comparison against ibrutinib in pts with WM.
Table 1. Table 1. Figure 1. Figure 1.
Disclosures
Tam: Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; janssen: Honoraria, Research Funding. Opat:Roche: Consultancy, Honoraria, Other: Provision of subsidised drugs, Research Funding. Simpson:Amgen Pharmaceuticals: Research Funding; Celgene, Roche, Janssen: Honoraria. Anderson:Walter and Eliza Hall Institute of Medical Research: Other: Walter and Eliza Hall Institute of Medical Research receives milestone payments for the development of venetoclax. Kirschbaum:Beigene: Employment. Wang:Beigene: Employment. Xue:Beigene: Employment. Yang:BeiGene: Employment. Hedrick:Beigene: Employment. Seymour:Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie Inc.: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees. Roberts:AbbVie: Research Funding; Servier: Research Funding; Genentech: Research Funding; Janssen: Research Funding; Genentech: Patents & Royalties: Employee of Walter and Eliza Hall Institute of Medical Research which receives milestone payments related to venetoclax.
High Major Response Rate, Including Very Good Partial Responses (VGPR), in Patients (pts) with Waldenstrom Macroglobulinemia (WM) Treated with the Highly Specific BTK Inhibitor Bgb-3111: Expansion Phase Results from an Ongoing Phase I Study