A multi-institution phase i trial of ruxolitinib in patients with chronic myelomonocytic leukemia (CMML)

Purpose: To conduct a phase I clinical trial exploring the safety and efficacy of ruxolitinib, a JAK1/2 inhibitor, for chronic myelomonocytic leukemia (CMML). Experimental Design: Patients with CMML-1 were included without regard to previous therapy. Key exclusion criteria included an absolute neutrophil count (ANC) <0.25 × 10³ cells/dL and a platelet count <35 × 10³ cells/dL. Four cohorts were enrolled using a "rolling six" study design, with doses ranging from 5 to 20 mg twice daily of ruxolitinib in 5-mg dose escalations. Results: Between March 2013 and January 2015, 20 patients were enrolled and treated with ruxolitinib. Seventy percent of patients had the proliferative subtype and 47% had higher risk disease by the Global MD Anderson Scoring System. Eight patients (42%) received a prior hypomethylating agent. No doselimiting toxicities for ruxolitinib were identified. One subject had grade (G)3 thrombocytopenia with no other drug-associated G3 or G4 adverse events. The mean duration of therapy was 122 days (range, 28-409 days). Four had hematologic improvement and one patient had a partial response per 2006 International Working Group (IWG) criteria. Five of 9 patients with splenomegaly had a reduction in spleen size. Ten of 11 patients with reported disease-related symptoms had clinically meaningful or complete resolution. When combining IWG and spleen responses, a total response rate of 35% (n =7) was identified. Correlative analysis demonstrated a reduction in inflammatory cytokines and GM-CSF-dependent STAT5 phosphorylation. Conclusions: The recommended phase II dose of ruxolitinib is 20 mg twice daily. We demonstrate that ruxolitinib has promising activity in CMML with particular benefit in those with disease-related B symptoms that warrants further study.