The present disclosure provides, in general, a method for selecting a therapy for treating cancer in a human subject and subsequently treating cancer in a subject, which includes isolating a cancer cell from a human subject having cancer, determining the functional activity of STING or cGAS in the cell; and selecting a therapy for the cancer based on the functional activity of the STING or cGAS in the cell. Also provided, if the functional activity of STING and/or cGAS is determined to be defective in the cell, the therapy selected is one that is effective at killing STING-deficient and/or cGAS-deficient cancer cells, e.g., therapy including administering to the subject an oncolytic virus.