Exercise can play a major role to mitigate or even prevent late effects in cancer survivors, such as cardiovascular disease, obesity, osteoporosis, fatigue, depression, reduced quality of life, mental health and physical performance.

The objective of this study is to assess the effect of an exercise program of 1 year on cardiovascular health, obesity and diabetes, osteoporosis, physical fitness, mental health and quality of life in childhood cancer survivors. The investigators will recruit childhood cancer survivors aged 16 years and above from three Swiss paediatric oncology clinics and randomize them into an intervention and a control group. The intervention group will be asked to increase physical activity for 1 year by at least 2.5 hours of intense physical activity weekly. Regular feedback will be given via a step counter, an online activity diary, and by the centre staff. The control group participants will keep their activity level constant. All participants will be seen after 3, 6 and 12 months to assess health and quality of life parameters over one year. After 1 year, the control group is offered to receive the same intervention to profit as well from an active lifestyle.

If the program shows to be effective, a complete package will become available to interested centres treating paediatric cancer patients in Switzerland to promote exercise in all survivors. The program will allow clinicians without previous experience in exercise counselling to improve the care of their patients.

Inclusion Criteria:

• Registered in the Swiss Childhood Cancer Registry.
• Age at cancer diagnosis <16 years.
• Diagnosed with a cancer classifiable within the International Classification of Childhood Cancer (ICCC-3) or diagnosed with a Langerhans Cell Histiocytosis.
• Diagnosed and/or treated at the University Children's Hospital Basel, Cantonal Hospital of Aarau and/or Cantonal Hospital of Lucerne.
• Survived ≥5 years since primary cancer diagnosis or any subsequent cancer event (relapse or further cancer diagnoses)
• Age at the time of the study ≥16 years
• Informed Consent as documented by signature

Exclusion Criteria:

• Participation in another clinical trial <4 weeks prior to baseline assessment (eventually later re-enrolment)
• Contradiction to one of the inclusion criteria mentioned above
• Inability to exercise
• Exercise potentially harmful
• Women who are pregnant or breast feeding
• Women who intend to become pregnant during the course of the study
• Instable clinical condition (eventually later re-enrolment)
• Under treatment for relapse or further cancer diagnoses
• Cardiac arrhythmias under exercise (during baseline assessment or by history)
• Diagnosis of diabetes <3 months ago (eventually re-enrolment after 3 months if diabetes is under good control)
• Detection of a clinical condition that needs immediate treatment during baseline assessments (eventually re-enrolment after 3 months if in stable clinical condition)
• Planned relevant surgeries for the next 12 months
• Major musculoskeletal injuries, fractures <2 months ago (eventually later re-enrolment)
• Recent change in medication that interfere with the parameters of the CVD risk score (primary outcome) <1 month ago (eventually later re-enrolment)
• >4 hours of reported vigorous activities per week
• Inability to follow the procedures and understand the intervention and assessments of the study e.g. due to cognitive impairment, language problems, psychological disorders etc.