Today, numerous data sources are available to healthcare professionals for diagnosing and treating cancer, but there are also data captured by patients, e.g. related to daily progress, which are not readily accessible to healthcare. In this workshop, we will use the critical incidents technique to inspire participants to elaborate on the need of using new data collections and measurements, for example from continuous self-tracking, as well as utilizing already existing data in new ways for diagnoses and treatment of cancer. Real-life critical incidents related to patients, healthcare professionals, and researchers, will be discussed and used as a basis for scenarios that will illustrate future visions of how self-reported data and self-measurements should be used in combination with existing data sources.