Obinutuzumab and Idelalisib in Symptomatic Patients with Relapsed/refractory Waldenström Macroglobulinemia

We present the results of a phase 2 study evaluating the combination of obinutuzumab + idelalisib in relapsed/refractory (R/R) Waldenström macroglobulinemia (WM). The goal was to determine the safety and efficacy of a fixed-duration chemotherapy-free treatment. During the induction phase, patients received idelalisib + obinutuzumab for 6 cycles, followed by a maintenance phase with idelalisib alone for ≤2 years. Forty-eight patients with R/R WM were treated with the induction combination, and 27 patients participated in the maintenance phase. The best responses, reached after a median of 6.5 months (interquartile range, 3.4-7.1; range, 2.6-22.1 months), were very good partial response in 5 patients, partial response in 27 patients, and minor response in 3 patients, leading to overall response rate and major response rate estimates of 71.4% (95% confidence interval [CI], 56.7-83.4) and 65.3% (95% CI, 50.4-78.3), respectively. With a median follow-up of 25.9 months, median progression-free survival was 25.4 months (95% CI, 15.7-29.0). Univariate analysis focusing on molecular screening found no significant impact of CXCR4 genotypes on responses and survivals but a deleterious impact of TP53 mutations on survival. Although there was no grade 5 toxicity, 26 patients were removed from the study because of side effects; the most frequent were neutropenia (9.4%), diarrhea (8.6%), and liver toxicity (9.3%). The combination of idelalisib + obinutuzumab is effective in R/R WM. Nonetheless, the apparent lack of impact of genotype on outcome could give new meaning to targeting of the phosphatidylinositol 3-kinase pathway in WM. This trial was registered at www.clinicaltrials.gov as #NCT02962401.