Provided is a method for treating cancer using a pyrazolo [3,4-d] pyrimidine compound or a salt thereof. Formula (I) wherein X, Y, Z 1 , Z 2 , Z 3 , Z 4 , W, n, R 1 , R 2 and R 3 have the meanings as defined in the specification. An antitumor agent, which is a combination of a pyrazolo [3,4-d] pyrimidine compound represented by or a salt thereof and another antitumor agent.ピラゾロ［３，４-ｄ］ピリミジン化合物又はその塩を用いた癌治療方法の提供。 一般式（Ｉ）［式中、Ｘ、Ｙ、Ｚ１、Ｚ２、Ｚ３、Ｚ４、Ｗ、ｎ、Ｒ１、Ｒ２及びＲ３は明細書中で定義したとおりの意味を有する］で表されるピラゾロ［３，４-ｄ］ピリミジン化合物又はその塩と、他の抗腫瘍剤を併用投与する抗腫瘍剤。
