The frequency of WM patients with MYD88L265P mutations achieving VGPR, as determined by an independent review committee, was numerically but not significantly higher in patients treated with zanubrutinib compared to ibrutinib on the phase III ASPEN study (28% vs 19% respectively, p = 0.09). No patient achieved CR. Investigator-assessed rates of VGPR were 28% and 17% in the zanubrutinib and ibrutinib arms, respectively (p = 0.04). It should be noted that the PFS outcome for patients treated with chemoimmunotherapy is similar between patients achieving VGPR and CR. The proportion of patients achieving VGPR in intermediate or high-risk groups based on the international prognostic scoring system (IPSS) were similar.
Best overall responses seen in the ASPEN trialr
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The proportion of MYD88L265P patients achieving MRR (at least a partial response with ≥ 50% reduction in IgM) was similar in those treated with zanubrutinib or ibrutinib (78% vs 80% in RR patients, 74% vs 67% in TN patients). The median time to major response for both arms was 2.8 months. The MRR was also comparable between CXCR4WHIM and CXCRWT patient subgroups with both zanubrutinib and ibrutinib. In the long-term follow-up of patients treated on the phase I/II BGB-311-AU003 study, the proportion of patients achieving VGPR/CR increased over time, with 21% of patients at six months compared to 49% of patients at 24 months, with evidence of a plateau at approximately 20 months.
Proportion of patients achieving VGPR or CR on treatment with zanubrutinibr
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Patients with MYD88WT disease treated in cohort 2 of the ASPEN study, demonstrated an overall MRR of 50% and OS of 81%. The median DOR was not reached in patients who had a response on study.
27% of patients achieved VGPR, and no patient achieved CR, which is similar to the proportion of MYD88L265P patients treated with zanubrutinib in cohort 1 of the ASPEN study. Relapsed refractory patients with MYD88WT WM had a MRR of 29% when treated with single-agent rituximabr, and a VGPR rate of 33% when treated with combination rituximab and ibrutinib in the INNOVATE study.r
The median PFS was not reached for either the ibrutinib or zanubrutinib arms in MYD88L265P WM patients treated in the ASPEN study, at a median follow-up of 19 months.r The estimated OS rates at 18 months were 97% and 93%, for ibrutinib and zanubrutinib, respectively. In patients with MYD88WT disease, the median PFS was not reached at a median follow-up of 18 months and the estimated OS rate at 18 months was 88%. In the long-term follow-up of MYD88L26P and MYD88WT patients treated on the phase I/II BGB3111-AU003 study, the median PFS was not reached after a median follow-up of 37 months and 23 months for RR and TN patients, respectively.