The purpose of the present invention is to provide cancer patients with chemotherapy using a PI3K/AKT/mTOR inhibitor that exhibits excellent anti-tumor effects. A method for predicting the therapeutic efficacy of chemotherapy, which uses an anti-tumor agent comprising a PI3K/AKT/mTOR inhibitor, in a cancer patient on the basis of the amount of expression of PHLDA1 and/or PIK3C2B in a biological sample comprising tumor cells collected from the cancer patient.