Ruxolitinib may yield clinical improvements, with moderate adverse events, among patients with myelofibrosis, according to results of a phase 3 trial published in the British Journal of Haematology.

The phase 3b JUMP study, which enrolled patients with myelofibrosis who were treated in a setting similar to that of routine clinical practice, is the largest study to date of ruxolitinib for this patient population. In this paper, the researchers presented the primary analysis of JUMP.

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Overall, 2233 patients were treated with the study protocol. The overall median age was 67 years, and 1217 patients (54.5%) were male; 60 (2.7%), 835 (37.4%), 755 (33.8%), 194 (8.7%), and 389 (17.4%) patients had low, intermediate-1, intermediate-2, high, and unknown disease risk, respectively, as determined using the dynamic International Prognostic Scoring System. Splenomegaly was reported in 1546 patients, and the mean spleen length at baseline was 13.3 cm.

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Median follow-up was 13.8 months, with a median length of drug exposure of 12.4 months. By week 24, 874 patients (56.5%) with splenomegaly had at least 50% reduction in palpable spleen length.

At 28 days after the study ended, 205 patients (9.2%) had died, suggesting a 96-week overall survival rate of 87%. The most common causes of mortality were myelofibrosis (38 patients), pneumonia (15 patients), septic shock (14 patients), and cardiac arrest (13 patients).

The most common grade 3 to 4 hematologic adverse events were anemia (34.8%), thrombocytopenia (19.3%), neutropenia (4.6%), and leukopenia (2.6%). The most common nonhematologic adverse events were pneumonia (4.7%), pyrexia (2.4%), asthenia (2.1%), and dyspnea (2%). Of the 138 patients with low platelet counts, 4 developed acute myeloid leukemia during the study.

“[R]uxolitinib provided clinically meaningful reductions in spleen size and symptoms” in this patient population, the researchers concluded.

Disclosures: Some authors have declared affiliations with the pharmaceutical industry. Please refer to the original study for a full list of disclosures.


1.     Al-Ali HK, Griesshammer M, Foltz L, et al. Primary analysis of JUMP, a phase 3b, expanded-access study evaluating the safety and efficacy of ruxolitinib in patients with myelofibrosis, including those with low platelet counts [published online February 4, 2020]. Br J Haematol. doi:10.1111/bjh.16462