Provided is a cancer treatment method that uses a pyrazolo[3,4-d]pyrimidine compound or a salt thereof. An antitumor agent that combines: a pyrazolo[3,4-d]pyrimidine compound represented by general formula (I) (in which X, Y, Z1, Z2, Z3, Z4, W, n, R1, R2, and R3 are as defined in the description) or a salt thereof; and another antitumor agent.本發明提供一種使用吡唑并[3,4-d]嘧啶化合物或其鹽之癌症治療方法。 本發明之抗腫瘤劑係將通式(I)[式中,X、Y、Z1、Z2、Z3、Z4、W、n、R1、R2及R3具有如說明書中所定義之含義]所表示之吡唑并[3,4-d]嘧啶化合物或其鹽與其他抗腫瘤劑併用投予。