Response to ruxolitinib in patients with intermediate-1-, intermediate-2-, and high-risk myelofibrosis: results of the UK ROBUST Trial

Myelofibrosis is characterized by splenomegaly and debilitating constitutional symptoms that negatively impact patients' quality of life. ROBUST, a UK, open-label, phase II study, evaluated the safety and efficacy of ruxolitinib in patients with myelofibrosis (N = 48), including intermediate-1 risk patients. The primary composite endpoint was the proportion of patients achieving treatment success [≥ 50% reduction in palpable spleen length and/or a ≥ 50% decrease in Myelofibrosis Symptom Assessment Form Total Symptom Score (MF-SAF TSS)] at 48 weeks. This was the first time that efficacy of ruxolitinib in myelofibrosis has been evaluated based on these criteria and the first time the MF-SAF was used in a population of patients solely from the United Kingdom. Overall, 50% of patients and 57% of intermediate-1 risk patients, achieved treatment success; reductions in spleen length and symptoms were observed in all risk groups. The majority of patients (66.7%) experienced ≥ 50% reductions from baseline in spleen length at any time. Improvements in MF-SAF TSS were seen in 80.0%, 72.7%, and 72.2% of intermediate-1, intermediate-2, and high-risk patients, respectively. Consistent with other studies of ruxolitinib, the most common haematological adverse events were anaemia and thrombocytopenia. Results indicate that most patients with myelofibrosis, including intermediate-1 risk patients, may benefit from ruxolitinib treatment.