Study of Selinexor in Combination With Ruxolitinib in Myelofibrosis

Inclusion Criteria:

• Aged ≥ 18 years

• A diagnosis of primary MF or post-essential thrombocythemia (ET) orpostpolycythemia- vera (PV) MF.

• Active symptoms of MF as determined by presence of at least 2 symptoms using theMyelofibrosis Symptom Assessment Form (MFSAF) V4.0.

• Participants with international prognostic scoring system (DIPSS) risk category ofintermediate-1, or intermediate-2, or high-risk.

• Measurable splenomegaly during the screening period as demonstrated by spleen volumeof greater than or equal to (>=) 450 cubic centimeter (cm^3) .

• Eastern Cooperative Oncology Group (ECOG) Performance Status less than or equal to (<=) 2.

Exclusion Criteria:

• More than 10% blasts in peripheral blood or bone marrow (accelerated or blastphase).

• Previous treatment with JAK inhibitors for MF.

• Previous treatment with selinexor or other XPO1 inhibitors.