The disclosure discloses the number of CD4 + OX40 + Foxp3 + lymphocytes in a sample containing cancer cells and lymphocytes obtained from a subject, labeling lymphocytes exhibiting expression of CD4 in the sample, and then in the sample Is measured by labeling lymphocytes showing expression of OX40, then labeling lymphocytes showing Foxp3 expression in the sample, and then measuring the number of CD4 + OX40 + Foxp3 + lymphocytes in the sample Provide a method. Based on the method of determining the prognosis of a subject and predicting the responsiveness of a subject with cancer to an OX40 agonist therapeutic agent and the number of CD4 + OX40 + Foxp3 + lymphocytes in a sample, or treating the progression of the cancer A method of delaying is further provided. [Selection] Figure 8C本開示は、対象から得られたがん細胞及びリンパ球を含有する試料中のCD4+ OX40+ Foxp3+リンパ球の数を、該試料中のCD4の発現を示すリンパ球を標識し、次いで、該試料中のOX40の発現を示すリンパ球を標識し、次いで、該試料中のFoxp3の発現を示すリンパ球を標識し、次いで、該試料中のCD4+ OX40+ Foxp3+リンパ球の数を測定することにより、測定する方法を提供する。対象の予後を判定し、がんを有する対象のOX40アゴニスト治療薬に対する応答性を予測する方法、及び試料中のCD4+ OX40+ Foxp3+リンパ球の数に基づいて、がんを治療する、またはその進行を遅延させる方法がさらに提供される。【選択図】図8C