Interventional oncology is a rapidly growing sub-speciality that aims to develop new disease-modifying treatment options beyond conventional surgical and oncological therapies in several disease settings. The evidence for interventional oncology success is dominated by single-arm studies reporting technical success or clinical efficacy. These studies have successfully resulted in the development of new techniques, but are not sufficient to change clinical practice uniformly across health-care systems. This Review discusses why clinical investigators must incorporate measures of cost-effectiveness and patient-reported outcomes into large-scale studies currently being designed to provide robust evidence for changing clinical practice. In particular, interventional oncology trials could be designed to show that certain treatments may be as effective as the current standard of care, but with significantly less morbidity and with better outcomes for patients with cancer. Innovative trial design and awareness of the challenges from interventional studies in other fields of medicine and surgery are also discussed to demonstrate how this new speciality can make progress. Registry-based models are emerging as an alternative means of deriving cohort data and can be used in parallel with local or national commissioning of new services.