Background
Phase 3, randomized, double-blind trial. 432 patients with high-risk, intermediate-2 risk, or symptomatic intermediate-1 risk MF who were JAK inhibitor (JAKi)-naïve. Momelotinib was compared to ruxolitinib as head-to-head first-line agents. After 24 weeks, all patients could receive open-label momelotinib. Noninferiority design for the primary endpoint.
Interventions and follow up
Arm A: Momelotinib 200 mg orally once daily (n≈216)
Arm B: Ruxolitinib 20 mg orally twice daily (or per label) (n≈216)
Primary endpoint: Spleen volume reduction ≥35% at 24 weeks (noninferiority margin prespecified)
Median follow up: 24 weeks (primary period)
Arm B: Ruxolitinib 20 mg orally twice daily (or per label) (n≈216)
Primary endpoint: Spleen volume reduction ≥35% at 24 weeks (noninferiority margin prespecified)
Median follow up: 24 weeks (primary period)
Results
SVR ≥35% at week 24: 26.5% (momelotinib) vs 29% (ruxolitinib) — NONINFERIOR (P=.011 for NI)
TSS ≥50% reduction: 28.4% vs 42.2% — noninferiority NOT met (P=.98)
Transfusion independence rate: Superior with momelotinib (nominal P≤.019)
Transfusion dependence rate: Lower with momelotinib
TSS ≥50% reduction: 28.4% vs 42.2% — noninferiority NOT met (P=.98)
Transfusion independence rate: Superior with momelotinib (nominal P≤.019)
Transfusion dependence rate: Lower with momelotinib
Adverse events
Hematologic (grade ≥3): Thrombocytopenia and anemia reported in both arms
Non-hematologic: Grade ≥3 infections 7% (momelotinib) vs 3% (ruxolitinib); treatment-emergent peripheral neuropathy 10% (momelotinib, all grade ≤2) vs 5% (ruxolitinib). Momelotinib was associated with worse infection rate and more peripheral neuropathy
Non-hematologic: Grade ≥3 infections 7% (momelotinib) vs 3% (ruxolitinib); treatment-emergent peripheral neuropathy 10% (momelotinib, all grade ≤2) vs 5% (ruxolitinib). Momelotinib was associated with worse infection rate and more peripheral neuropathy
Conclusions
Momelotinib was noninferior to ruxolitinib for spleen volume response but failed to demonstrate noninferiority for symptom response, suggesting inferior symptomatic control. However, momelotinib produced superior improvements in transfusion-related outcomes, supporting its utility specifically in anemia-predominant MF.
Key Limitations
The trial failed its TSS noninferiority endpoint, a clinically meaningful limitation. Peripheral neuropathy was more common with momelotinib. Higher infection rates with momelotinib vs ruxolitinib (7% vs 3% grade ≥3) are noteworthy. The spleen NI threshold was met, but this was the less clinically meaningful of the two endpoints. The open-label crossover after week 24 obscures long-term OS comparisons. Results reflect an early JAKi-naïve population; utility in later lines was assessed in MOMENTUM.
Clinical Context
SIMPLIFY-1 established momelotinib as approximately equivalent to ruxolitinib for spleen reduction but less effective for symptom control in first-line MF. Its key advantage — superiority in transfusion outcomes — was a secondary endpoint here but became the primary value proposition in MOMENTUM. Based on the totality of SIMPLIFY-1 and MOMENTUM data, momelotinib received FDA approval in 2023 specifically for MF with anemia. Ruxolitinib remains the preferred first-line agent for most patients per ESMO; momelotinib is preferred when significant anemia dominates.