Six-year follow-up of phase II study exploring chemo-free treatment association with idelalisib and obinutuzumab in symptomatic relapsed/ refractory patients with Waldenström's macroglobulinemia

We present the 6-year update of a phase 2 study evaluating the combination of obinutuzumab and idelalisib in relapse/refractory Waldenstrom macroglobulinemia. The results of the REMODEL trial demonstrated interesting efficacy in a high-risk genotype profile population. The primary endpoint was achieved with a median PFS of 25.4 months (95% CI, 15.7 to 29.0). However, a major limitation of idelalisib is its toxicity. With a median follow-up of 70.9 months, median OS was still not reached, and 5-year OS was 72.9% (95% CI, 61.3 to 86.6). We confirm that CXCR4 mutations had no impact on PFS or OS. However, TP53 mutated patients had shorter OS. At the time of analysis, six patients are alive without relapse and 40 had progressive disease. Among the 38 patients who received a new treatment, the median time to second progression was not reached in ibrutinib treated patients (n = 17) versus 30.8 months in patients treated with other options (95% CI, 16.9 to NA), p = 0.005. With longer follow-up our prospective study is the first to show an impact of TP53 mutations in patients treated with fixed duration chemo-free regimen leading to a significant shorter OS in this population. Moreover, ibrutinib remains an effective treatment after this combination. This study was registered on the clinicaltrial.gov web (NCT02962401, November 9, 2016).