Systemic Treatment Related Toxicity Identified With a Smartphone APPlication Measuring Step Count

The goal of this observational study is to investigate whether daily physical activities measured with a smartphone are related to the possible side effects or other physical complaints that arise as a result of cancer treatment. The investigators want to test whether the number of steps per day, both before and during treatment, are related to possible side effects or other physical complaints of the treatment using a smartphone. Knowledge about this relationship gives us possible starting points to prevent and/or reduce side effects and improve treatment outcomes. Additional research would then be needed. The investigators also want to investigate whether these daily measurements are feasible for patients undergoing treatment. Participation in the study involves measuring daily physical activity from the week before treatment until the first 3 months of treatment have been completed. This is done by tracking daily steps with patients own phone using the OncoSTAPP application.