Provided herein are compositions and methods for treating myelofibrosis in a subject. The methods comprise administering to the subject an effective amount of compound which is which is N-tert-butyl-3-[(5-methyl-2-{[4-(2-pyrrolidin-1-ylethoxy)phenyl]amino}pyrimidin-4-yl)amino]benzenesulfonamide or a pharmaceutical salt thereof or a hydrate thereof.本文提供治療個體之骨髓纖維化的組合物及方法。該等方法包含投與該個體有效量之化合物N-第三丁基-3-[(5-甲基-2-{[4-(2-吡咯啶-1-基乙氧基)苯基]胺基}嘧啶-4-基)胺基]苯磺醯胺或其醫藥鹽或其水合物。