Selinexor in Myelofibrosis Refractory or Intolerant to JAK1/2 Inhibitors

Inclusion Criteria: * Male or female subject aged ≥ 18 years. * Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2 * Diagnosis of primary myelofibrosis (PMF), post-essential thrombocytosis (PET-MF) or post-polycythemia vera (PPV-MF). * Life expectancy ≥ 6 months. * Prior treatment with ruxolitinib or any experimental JAK1/2 inhibitor with any one or more of the following: a. Inadequate response after being on ≥ 3 months of treatment defined by: i. Palpable spleen ≥ 10 cm below the left subcostal margin on physical examination at the screening visit OR ii. Palpable spleen ≥ 5cm below the left subcostal margin on physical examination at the screening visit AND active symptoms of MF at the screening visit defined presence of 1 symptom score of ≥ 5 or two symptom scores each of ≥ 3 using the Screening Symptoms Form (Appendix 6) b. Intolerant to ruxolitinib and/or other JAK1/2 inhibitors due to any grade ≥ 3 non-hematologic AEs of or any grade ≥ 2 AEs requiring treatment discontinuation AND palpable spleen ≥ 5cm below the left subcostal margin on physical examination at the screening visit. * Adequate organ function as defined as: * Hematologic (≤ 28 days prior to C1D1): * Total white blood cell (WBC) count ≥ 1000/mm3 * Absolute neutrophil count (ANC) ≥ 500/mm3 * Hemoglobin ≥ 7 g/dL * Platelet count ≥ 30,000/mm3 For patients receiving transfusion and growth factor support, the following delays must be observed between the last administration …