The present invention relates to methods and materials for more effectively treating patients with interferon. It is based on the discovery that clinical response to interferon (IFN) therapy is mediated in part by inhibition of activation of MDSC and such inhibition can be observed after a test dose of interferon a significant decrease of reactive oxygen species (ROS) production by MDSC (as a measure of their activation) after IFN therapy is predictive of overall response to immunotherapy in cancer patients.
