The present invention provides: a method for identifying a blood cancer patient who may benefit from a monotherapy using a drug comprising a DNA methyl transferase inhibitor and a combination therapy using the aforesaid drug together with another epigenetic controller; a pharmaceutical composition to be used in treating a patient who has been identified or selected by the method; and a kit for identifying such a patient. More particularly, the aforesaid method comprises a step for measuring the expression amount of DUSP5 in a sample obtained from a blood cancer patient. When the expression amount measured in this step is lower than a reference expression amount of DUSP5, then the patient is identified or selected as a blood cancer patient who may benefit from a treatment using the drug comprising a DNA methyl transferase inhibitor.