Response and survival predictors in a cohort of 319 patients with Waldenström macroglobulinemia treated with ibrutinib monotherapy.

Bruton tyrosine kinase (BTK) inhibitors are the only FDA-approved treatments for Waldenström macroglobulinemia (WM). Factors prognostic of survival and predictive of response to BTK inhibitors remained to be clarified. We evaluated 319 patients with WM to identify predictive and prognostic factors on ibrutinib monotherapy. Logistic and Cox proportional-hazard regression models were fitted for response and survival. Multiple imputation analyses were used to address bias associated with missing data. Major (partial response or better) and deep responses (very good partial response or better) were attained in 78% and 28% of patients. CXCR4 mutations were associated with lower odds of major (odds ratio [OR], 0.2; 95% confidence interval [CI], 0.1-0.5; P < .001) and deep response (OR, 0.3; 95% CI, 0.2-0.6; P = .001). CXCR4 mutations (hazard ratio [HR], 2.0; 95% CI, 1.2-3.4; P = .01) and platelet count 100 K/uL or less (HR, 2.5; 95% CI, 1.3-4.9; P = .007) were associated with worse progression-free survival (PFS). We proposed a scoring system using these 2 factors. The median PFS for patients with 0, 1, and 2 risk factors were not reached, 5 years and 3 years (P < .001). Patients with 2 risk factors had HR 2.2 (95% CI, 1.3-3.8; P = .004) compared with 1 factor, and patients with 1 factor had HR 2.3 (95% CI, 1.1-5.1; P = .03) compared with 0 factors. Age ≥65 years was the only factor associated with overall survival (HR, 3.2; 95% CI, 1.4-7.0; P = .005). Multiple imputation analyses did not alter our results. Our study confirms the predictive and prognostic value of CXCR4 mutations in patients with WM treated with ibrutinib monotherapy.

Phase 1 study of ibrutinib and the CXCR4 antagonist ulocuplumab in CXCR4-mutated Waldenström macroglobulinemia.

MYD88 and CXCR4 mutations are common in Waldenström macroglobulinemia (WM). Mutated CXCR4 (CXCR4Mut) impacts BTK-inhibitor response. We conducted a phase 1 trial of the CXCR4-antagonist ulocuplumab with ibrutinib in this first-ever study to target CXCR4Mut in WM. Ibrutinib was initiated at 420 mg/d with cycle 1 and continued until intolerance or progression; ulocuplumab was given cycles 1 to 6, with a 3 + 3 dose-escalation design. Each cycle was 4 weeks. Thirteen symptomatic patients, of whom 9 were treatment-naive patients were enrolled. Twelve were evaluable for response. At best response, their median serum immunoglobulin M declined from 5574 to 1114 mg/dL; bone marrow disease decreased from 65% to 10%, and hemoglobin increased from 10.1 to 14.2 g/dL (P < .001). The major and VGPR response rates were 100% and 33%, respectively, with VGPRs observed at lower ulocuplumab dose cohorts. Median times to minor and major responses were 0.9 and 1.2 months, respectively. With a median follow-up of 22.4 months, the estimated 2-year progression-free survival was 90%. The most frequent recurring grade ≥2 adverse events included reversible thrombocytopenia, rash, and skin infections. Ulocuplumab dose-escalation did not impact adverse events. The study demonstrates the feasibility of combining a CXCR4-antagonist with ibrutinib and provides support for the development of CXCR4-antagonists for CXCR4Mut WM. This trial was registered at www.clinicaltrials.gov as #NCT03225716.