A method of treating lymphoma in a mammal comprises the step of: administering to a patient a pharmaceutical acceptable amount of a compound being a 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)q-R8 wherein R 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. The lymphoma to be treatzed is diffuse large B-cell lymphom (DLBCL) specifically selected from activated B-cell DLBCL (ABC-DLBCL) and germinal B-cell DLBCL (GBC-DLBCL).
