Momelotinib During and After HCT in Myelofibrosis

Inclusion Criteria: * Participants must have pathologically confirmed primary myelofibrosis (PMF) according to WHO criteria or secondary myelofibrosis as defined by the IWG-MRT criteria. * Intermediate-2/ high-risk disease as per Dynamic IPSS (DIPSS) Plus criteria OR * Intermediate-1 risk disease with at least one of the following unfavorable features known to impact the survival adversely * Red cell transfusion dependency * Unfavorable Karyotype * Platelet count ≤100 x 10\^9/L * Presence of a high risk molecular marker associated with worsened overall survival (ASXL1, EZH2, IDH1/2, SRSF2, U2AF1, p53) * Participants do not have to be receiving treatment with JAK inhibitors for MF at the time of enrollment. If participants are receiving JAK inhibitor therapy with agents other momelotinib, participants must agree to be switched to momelotinib to begin Cycle 1 Day 1 on Day -7 from HCT (at the initiation of conditioning). * Age \>18 years * Participants must be designated to undergo allogeneic HCT with: * reduced intensity conditioning regimen, and * peripheral blood stem cells as a graft source * Participants who will undergo HCT from the following donor types are eligible: * 6/6 (HLA-A, B, DR) fully matched related donor or * 8/8 (HLA-A, B, DR, C) fully matched unrelated donor. Matching in the unrelated setting must be at the allele level * ECOG performance status ≤2 (Karnofsky ≥60%) * The effects of momelotinib on the developing human fetus are…