Ruxolitinib Pre-, During- and Post-HSCT for Patients With Primary or Secondary Myelofibrosis.

Inclusion Criteria: * Participants must have pathologically confirmed primary myelofibrosis according to WHO criteria or secondary myelofibrosis as defined by the IWG-MRT criteria. * Intermediate-2/ high-risk disease as per Dynamic IPSS (DIPSS) criteria (Appendix G) OR * Intermediate-1 risk disease with one of the following additional 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) * Age 18-75 * Participants must be designated to undergo reduced intensity allogeneic peripheral blood (PB) or bone marrow (BM) hematopoietic stem cell transplantation. Consent will be obtained prior to admission for HCT. * Participants who will undergo HCT from the following donor types are eligible: * 6/6 (HLA-A, B, DR) fully matched related donor * 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%, see Appendix A) * Life expectancy of greater than 3 months * Able to give informed consent * Off all MF-directed therapy at the time of enrollment, with the exception of ruxolitinib, one week or 4 half-lives (effective), whichever is longer, prior to the first dose of study treatment * No allergy to ruxolitinib in the past * For patients already recei…