ABSTRACT
The phase 3 MOMENTUM study (NCT04173494) of the ACVR1/JAK1/JAK2 inhibitor momelotinib (MMB) vs. danazol (DAN) in patients with myelofibrosis (MF) previously treated with a JAK inhibitor (JAKi) met the primary endpoint and all key secondary endpoints at week 24 (W24). We provide updated results from week 48 assessments. Eligible patients had primary or post-ET/ PV MF;DIPSS high, Int-2, or Int-1 risk;Total Symptom Score (TSS) >=10;haemoglobin (Hb) <10 g/dL;platelets >=25 x 109/L;prior JAKi for >=90 days (>=28 days if red blood cell [RBC] transfusions >=4 units in 8 weeks or grade 3/4 thrombocytopenia/anaemia/ hematoma);and palpable spleen >=5 cm. Randomisation was 2:1 to MMB 200 mg/day or DAN 600 mg/day for 24 weeks, followed by open-label (OL) MMB. Week 48 endpoints included durations of response (TSS, transfusion independence [TI], splenic) and overall and leukaemia-free survival (OS, LFS). As of 17 May 2022, 93/130 (72%) MMB -> MMB and 41/65 (63%) DAN -> MMB patients received OL MMB;mean MMB durations were 48 weeks and 24 weeks, respectively. Analyses for W24 responders showed the following: of TSS responders, 31/32 (97%) MMB -> MMB and 6/6 DAN -> MMB patients had TSS < baseline;of TI responders, 36/40 (90%) and 10/13 (77%) had no RBC transfusions or Hb <8 g/dL;and of spleen responders, all patients had splenic volume < baseline. In the OL phase, the most common grade >=3 treatment-emergent adverse events (TEAEs) were thrombocytopenia (MMB -> MMB, 9%;DAN -> MMB, 15%) and anaemia (MMB -> MMB, 9%;DAN -> MMB, 2%). Grade >=3 infections occurred in 19% of MMB -> MMB and 10% of DAN -> MMB patients, including grade >=3 (nonfatal) COVID-19. Peripheral neuropathy (PN) occurred in 2% of patients in each arm, and none discontinued MMB due to PN. TEAEs led to MMB discontinuation in 18% (MMB -> MMB) vs. 10% (DAN -> MMB). A trend towards improved OS up to W24 was previously observed with MMB vs. DAN (hazard ratio [HR], 0.506;p = 0.0719);after all patients crossed over to OL MMB, OS and LFS curves for both arms converged (HR, 0.945, 95% CI, 0.528-1.693;HR, 0.830, 95% CI, 0.473-1.4555). Sixty of 81 (74%) MMB -> MMB and 29 of 43 (67%) DAN -> MMB patients with baseline platelets <=150 x 109/L entered the OL phase. Efficacy and safety results in thrombocytopenic subgroups in the OL period were consistent with the intent-to- treat (ITT) population. OL MMB maintained symptom, TI, and spleen responses with continued good survival and safety in the ITT and low platelet populations. MMB may address an unmet need in anaemic patients with MF.