A phase 1b study of ibrutinib in combination with obinutuzumab in patients with relapsed or refractory chronic lymphocytic leukemia

This study investigated ibrutinib plus obinutuzumab in relapsed/refractory CLL, evaluating tolerability of 3 sequencing regimens as well as overall safety and efficacy. Fifty-two patients were initially randomized 1:1:1 to receive either obinutuzumab 1 month before ibrutinib initiation, ibrutinib 1 month prior to obinutuzumab initiation, or to start both drugs concomitantly. Higher rates of infusion-related reactions were observed with the first sequence, and only the latter 2 cohorts were expanded. Grade 4 hematologic toxicity was uncommon, and notable all-grade non-hematologic toxicities included bruising (58%), hypertension (46%), arthralgia (38%), diarrhea (37%), transaminitis (35%), atrial fibrillation (21%), and serious infection (17%). Best overall response rate was 96% (including 40% CR and 56% PR). Best rates of undetectable minimal residual disease in peripheral blood and bone marrow were 27% and 19%, respectively. With a median follow-up of 41.5 months, four-year progression-free and overall survival rates are 74% and 93%, respectively. Correlative studies demonstrated that serum CCL4 and CXCL13 levels were associated with clinical response, and BH3 profiling revealed increased BCL-2 and BCL-xL dependence in CLL cells from patients on treatment. Overall, ibrutinib plus obinutuzumab was highly active, with a manageable safety profile, supporting further investigation of this type of approach in relapsed/refractory CLL.