Professor Robert Thomas, an oncologist from Cambridge University Hospitals NHS Foundation Trust, said more needed to be done to drive up survival rates and lower the side-effects of treatment through healthy eating, exercise and dropping pounds.
He said people were relying too much on vitamins and supplements, with little evidence they worked, rather than doing simple things like taking brisk walks.
There was a lot of discussion around cancer treatments and expensive new drugs when the “elephant in the room” was what patients can do to help themselves, he added.
Research shows that healthy lifestyles give cancer patients a better chance of coping with gruelling treatment alongside improved moods and fewer side-effects.
Data also shows that steps such as taking exercise and keeping to a healthy weight can cut the chance of the disease coming back.
Prof Thomas said: “There is a lot of focus on cancer drugs that extend lives by a matter of months but not enough emphasis on what people can do to help themselves.
“We know that three hours of exercise per week after most cancers will reduce the chance of relapse by up to 30 per cent.
“Yet very little time is spent discussing lifestyle issues compared to extensive deliberations about chemotherapy, which in some cases only offers a 5 per cent benefit.”
Prof Thomas’s study on 120 patients found only 11 per cent of patients were doing any exercise during recovery from cancer, while 68 per cent were overweight or obese.
Some people feared they would make their fatigue worse or were worried about other effects, and were not fully aware of the benefits, he said.
Others simply ignored healthy living advice.
“Many people think that instead of going to the gym, they can grab a whole load of supplements and that will do the job for them,” he added.