A method of treating leukemia in a mammal by administering a solid dispersion comprising an amorphous thienotriazolodiazepine compound of the Formula (1) wherein R1 is alkyl having a carbon number of 1-4, R2 is a hydrogen atom; a halogen atom; or alkyl having a carbon number of 1-4 optionally substituted by a halogen atom or a hydroxyl group, R3 is a halogen atom; phenyl optionally substituted by a halogen atom, alkyl having a carbon number of 1-4, alkoxy having a carbon number of 1-4 or cyano; —NR5—(CH2)m—R6 wherein R5 is a hydrogen atom or alkyl having a carbon number of 1-4, m is an integer of 0-4, and R6 is phenyl or pyridyl optionally substituted by a halogen atom; or —NR7—CO—(CH2)n—R8 wherein R7 is a hydrogen atom or alkyl having a carbon number of 1-4, n is an integer of 0-2, and R8 is phenyl or pyridyl optionally substituted by a halogen atom, and R4 is —(CH2)a—CO—NH—R9 wherein a is an integer of 1-4, and R9 is alkyl having a carbon number of 1-4; hydroxyalkyl having a carbon number of 1-4; alkoxy having a carbon number of 1-4; or phenyl or pyridyl optionally substituted by alkyl having a carbon number of 1-4, alkoxy having a carbon number of 1-4, amino or a hydroxyl group or —(CH2)b—COOR10 wherein b is an integer of 1-4, and R10 is alkyl having a carbon number of 1-4, or a pharmaceutically acceptable salt thereof or a hydrate or solvate thereof.