The present disclosure provides methods for predicting responsiveness of a subject having cancer to an OX40 agonist treatment by measuring the expression level of one or more biomarkers. Also provided are methods for monitoring pharmacodynamic activity of or responsiveness to an OX40 agonist treatment by measuring the expression level of one or more biomarkers. Further provided are methods related thereto for treating or delaying progression of cancer in a subject by administering an effective amount of an OX40 agonist to a subject. Specific biomarkers for all such methods are described herein.