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.FORMULACIÓN ORAL QUE COMPRENDE DICLORHIDRATO DE N-TERC-BUTIL-3-[(5-METIL-2-{[4-(2-PIRROLIDIN-1-ILETOXI)FENIL]AMINO}PIRIMIDIN-4-IL)AMINO]BENCENOSULFONAMIDA MONOHIDRATO, UNA CELULOSA MICROCRISTALINA Y ESTEARIL FUMARATO DE SODIO; MÉTODO PARA SU PREPARACIÓN; Y SU USO PARA TRATAR MIELOFIBROSIS.