Exercise is a "wonder drug" for cancer survivors and may even prevent the disease coming back, a report says.
Macmillan Cancer Support said physical activity should be "prescribed" by doctors after "hard evidence" showed it can significantly help recovery and prevent other long-term illnesses.
Rather than patients being told to "rest up" as in the past, doctors must encourage people to get moving as soon as they feel able.
A review of more than 60 studies for the charity found people undergoing treatment for cancer – as well as survivors – could benefit from exercise.
During treatment, being active does not worsen people's fatigue and has positive effects on mood and wellbeing, the study said. Once treatment has finished, exercise can reduce the impact of side effects, such as swelling around the arm, anxiety, depression, fatigue, impaired mobility and changes to weight.
"Long term, it is an effective way to help recover physical function, manage fatigue, improve quality of life and mental health, and control body weight," the report said.
It also showed exercise had an impact on preventing recurrence of specific cancers, including breast, bowel and prostate cancers.