Financial toxicity as an individual consequence of a cancer diagnosis currently evolves to a clinically relevant patient-reported outcome, as several US studies showed that financial burden from cancer patients could impact the quality of life and mortality significantly. However, there is only limited data about financial burden on patients from universal healthcare countries and, in particular, Germany. One reason for this is the lack of a standardised and validated German-language survey instrument to measure financial toxicity precisely. This study aims to develop such an appropriate instrument.