Stimulator of interferon genes (STING) has been shown to be critical for controlling antiviral responses as well as anti-tumor adaptive immunity, but little is known regarding its regulation in human tumors. Here, we report that STING signaling is recurrently suppressed in a wide variety of cancers, including colorectal carcinoma. Loss of STING signaling impeded DNA damage responses accountable for generating key cytokines that facilitate tissue repair and anti-tumor T cell priming, such as type I interferons (IFNs). Correspondingly, defective STING function was also highly predictive of effectual DNA-virus-mediated oncolytic activity. Thus, impaired STING responses may enable damaged cells to evade host immunosurveillance processes, although they provide a critical prognostic measurement that could help predict the outcome of effective oncoviral therapy.