The Mio study (Metacognitive Intervention in Youth with Oncological Disease) is a randomized clinical study to test the effectiveness of a novel metacognitive training app at the interface between neuropsychology and sport. The study is being carried out by the University Hospital of Bern, Inselspital (Prof. Regula Everts) together with the Institute for Sports Science at the University of Bern. All study participants need access to the Mio app.