Reduced Intensity Haploidentical Transplantation for the Treatment of Primary or Secondary Myelofibrosis

Inclusion Criteria: * PART 1: JAK INHIBITOR ADMINISTRATION INCLUSION CRITERIA * Age between 18 and 70 years * Diagnosis of primary myelofibrosis (PMF) as defined by the 2016 World Health Organization classification system or diagnosis of secondary MF as defined by the International Working Group (IWG) for Myeloproliferative Neoplasms Research and Treatment criteria * Patients meeting the criteria for intermediate-1, intermediate-2 or high-risk disease by the Dynamic International Prognostic Scoring System (DIPSS)-plus scoring system (DIPSS may be used if all data from DIPSS are not available) * Ability to understand and the willingness to sign a written informed consent document (or legally authorized representative) * Patient must be a potential hematopoietic stem cell transplant candidate * PART 2: ALLOGENEIC STEM CELL TRANSPLANT INCLUSION CRITERIA * Meeting criteria for 1st phase as above, at time of initiation of JAK inhibitor, including ability to understand and willingness to sign a written informed consent (or legally authorized representative). Patients arriving to our institution for transplant and not enrolled in Part 1 may still be enrolled in Part 2 if Part 1 criteria met. These patients will have Part 1 endpoints transcribed from medical records * Received JAK inhibitor for at least 8 weeks immediately prior to conditioning and be willing to continue until 9-12 months post-transplant as tolerated * Karnofsky performance status score \>= 70 * Calculated creatinin…