Safety and Efficacy of Ruxolitinib for the Final Enrollment of JUMP: An Open-Label, Multicenter, Single-Arm, Expanded-Access Study in Patients with Myelofibrosis (N = 2233)

BACKGROUND: Ruxolitinib is a potent JAK1/JAK2 inhibitor that has proved superior to placebo and best available therapy in the phase 3 COMFORT studies for patients (pts) with intermediate (Int)-2- or high-risk myelofibrosis (MF). Ruxolitinib-treated pts demonstrated improvements in splenomegaly and MF-related symptoms as well as improved overall survival. JUMP is an expanded-access phase 3b trial designed to assess the safety and efficacy of ruxolitinib in pts with MF and includes those with no access to ruxolitinib outside of a clinical trial. Here, we report updated safety and efficacy findings for the full enrollment of JUMP, which includes 2233 pts in 26 countries.

METHODS: Eligible pts had Int-2- or high-risk MF, with or without splenomegaly, or Int-1-risk MF with a palpable spleen (≥ 5 cm from the costal margin). Pts received starting doses of ruxolitinib based on platelet counts at baseline (5 mg twice daily [bid; ≥ 50 to < 100 × 10⁹/L], 15 mg bid [100 to 200 × 10⁹/L], 20 mg bid [> 200 × 10⁹/L]). The primary endpoint was assessment of safety and tolerability of ruxolitinib. Additional analyses included changes in palpable spleen length and symptom scores. The final analysis will be performed after all pts have completed 24 months of treatment or discontinued the study.

RESULTS: This analysis includes 2233 pts (primary MF, 59.4% [n = 1326]) who started treatment ≥ 1 year before the data cutoff date (01 Jan 2016). At baseline, median age was 67 y (range, 18-89 y); 54.5% were male; median palpable spleen length was 12 cm below the costal margin; median time since diagnosis was 25.8 months. Median hemoglobin (Hb) was 106 g/L, and 38.3% of pts had Hb levels ˂ 100 g/L; median platelet count was 254 × 10⁹/L; mean FACT-Lym TS and FACIT-Fatigue score were 113.9 and 33.4, respectively. At data cutoff, 15.8% of pts (353/2233) remained on treatment and 45.1% (1006/2233) completed treatment per protocol (ie, transitioned to commercial ruxolitinib). The primary reasons for treatment discontinuation were adverse events (AEs; 17.7%), disease progression (8.6%), and death (4.1%).

Median exposure was 12.4 months; the median average daily dose of ruxolitinib was 23.1 mg for pts starting at 15 mg bid (n = 647 [29.0%]) and 36.5 mg for pts starting at 20 mg bid (n = 1384 [61.9%]). Overall 66.7% of pts had dose modifications and 26.3% had a dose interruption. Grade (G) 3/4 hematologic AEs included anemia (34.1%), thrombocytopenia (16.3%), and neutropenia (4.5%), which led to discontinuation in 1.5%, 2.7%, and 0.1% of pts, respectively. Nonhematologic AEs were primarily G1/2, and the most common (≥ 10%) were pyrexia (15.6%; G3/4, 2.3%), asthenia (14.9%; G3/4, 2.2%), and diarrhea (12.0%; G3/4, 1.1%). Rates of other G3/4 AEs were low (≤ 2%), except pneumonia (4.3%), which led to discontinuation in 10 pts (0.5%). Rates of infections were generally low; all-grade infections in ≥ 5% of pts included pneumonia (6.8%), urinary tract infection (5.6%), and nasopharyngitis (5.0%). Herpes zoster was reported in 4.6% of pts (G3/4, 0.5%), tuberculosis in 0.2% (G3/4, 0.04%) and hepatitis B in 1 pt (G3/4, 0.04%).

At wk 24 and 48, 56.6% (874/1545) and 61.6% (658/1069) of pts with baseline splenomegaly achieved a ≥ 50% reduction from baseline in palpable spleen length; 23.3% (360/1545) and 18.9% (202/1069) had 25% to 50% reductions, respectively. Most pts (70.2% [1441/2054]) experienced a ≥ 50% reduction at any time; 23.7% had complete resolution of splenomegaly (Figure). At wk 24 and 48, 97.1% (67/69) and 92.3% (48/52) of evaluable pts without splenomegaly at baseline continued to have a nonpalpable spleen. A large proportion of pts achieved a response (ie, a clinically significant improvement) on the FACT-Lym TS and FACIT-Fatigue at wk 24 (42.4% [596/1406]; 46.6% [675/1447]) and wk 48 (42.9% [404/941]; 45.4% [434/957]). Overall, 221 patients received ESAs to manage anemia (G1, 7.2%; G2, 49.8%; G3, 38.9%; G4, 4.1%), and the majority had improved (32.6%) or resolved (31.7%) anemia (worsened, 16.3%; no change, 19.5%).

CONCLUSIONS: This study includes the largest cohort of pts with MF treated with ruxolitinib to date. Consistent with findings from other studies, anemia and thrombocytopenia were the most common AEs but rarely led to discontinuation. As observed previously, most pts experienced reductions in splenomegaly and symptoms with ruxolitinib treatment. Overall, the safety and efficacy profile of ruxolitinib in JUMP is consistent with that in the COMFORT studies.

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