Measuring and defining screening benefit in a new era of cancer early detection

We are at a watershed moment in the history of early cancer detection in which many novel tests are poised to become available for population screening. An ongoing debate concerns how to properly evaluate these tests and specifically whether a shorter-term, incidence-based outcome might substitute for cancer mortality as an endpoint in randomized trials of screening test efficacy. An incidence-based endpoint promises to reduce time and resources, but there is no framework for how studies using this endpoint should report results and how they should be interpreted in terms of clinical utility. We consider whether publication of incidence-based results ahead of any mortality results could result in adoption of new screening tests ahead of reliable mortality results becoming available. We argue that guardrails are needed for this scenario, including standards for conduct and reporting of trials with incidence-based endpoints to assure valid interpretation of clinical utility. For example, information regarding the type and timing of tests used for diagnostic workup in screen and control groups will be needed. Clinicians and policy makers will need to determine acceptable measurements and magnitudes of this modified measure of test efficacy. The roles of incidence-based and mortality-based endpoints in determining practice standards will need to be defined, along with specifications for permissible adjunct evidence, such as modeling studies and real-world data. As screening trials for new multi-cancer tests will soon begin to report incidence-based results, resolution of these questions is a matter of urgency.