Almost 2.5 million deaths worldwide from cancer could be prevented if people changed their diet and behaviour, say researchers.
Nine factors account for more than a third of the 7 million cancer deaths a year that could be avoided.
Reducing smoking, cutting alcohol use and increasing fruit and vegetable consumption are the most important factors but too little effort is going into promoting their life-saving effects, researchers say.
Writing in the Lancet medical journal, scientists from the United States, Australia and New Zealand say the obsession with curing cancer has prevented progress in the war against the disease, whose incidence is growing around the globe.
Although screening and treatment are proving increasingly effective in reducing the death toll, their benefits are limited by cost and the difficulty of getting access to them in many countries.
"Advances in cancer treatment have not been as effective as those for other chronic diseases. Primary prevention through lifestyle and environmental interventions remains the main way to reduce the burden of cancer," they write.
Smoking is the most important risk factor and is estimated to have caused 21 per cent of deaths from cancers worldwide.
Alcohol use and low fruit and vegetable consumption are the next most important, each accounting for 5 per cent of cancer deaths.
Smoking mainly causes lung cancer, accounting for 70 per cent of the 1.2 million deaths from the disease. But it is also a cause of eight other cancers: mouth (42 per cent of deaths), oesophagus (42 per cent), stomach (13 per cent), liver (14 per cent), pancreas (22 per cent), cervix (2 per cent), bladder (28 per cent) and leukaemia (9 per cent).
Alcohol causes four cancers: oesophagus (26 per cent of deaths), liver (25 per cent), mouth (16 per cent) and breast (5 per cent).
Other risk factors include obesity, which accounts for 11 per cent of colon cancer deaths and 40 per cent of deaths from cancer of the uterus.
Physical inactivity increases the risk of breast cancer, accounting for 10 per cent of all deaths from the disease, and of colon cancer (15 per cent of deaths).
Low fruit and vegetable consumption is a factor for four cancers: oesophagus (18 per cent of deaths), stomach (18 per cent), colon (2 per cent) and lung (11 per cent).
Sex without a condom leads to transmission of the human papilloma virus, which causes 100 per cent of cases of cervical cancer, a major killer in the developing world. Cervical cancer causes 234,000 deaths worldwide, over 90 per cent in low- and middle-income countries.
Air pollution, which is worst in the developing world, and smoke from open fires and solid fuel cookers with inadequate ventilation increase the risk of lung cancer.
The practice of reusing needles for medical injections in the developing world transmits hepatitis and other viruses that cause liver cancer.
The nine risk factors studied caused twice as many cancer deaths in men as in women.
Majid Ezzati from the Harvard School of Public Health, who led the study, said: "Primary prevention through lifestyle and environmental interventions remains the main route for reducing the global cancer burden. If implemented, reduction of exposure to well-known behavioural and environmental risk factors would prevent a substantial proportion of deaths from cancer."
* A blood test to predict an individual's risk of developing cancer could be available in the next decade.
Professor Karol Sikora, from Imperial College, London, and Hammersmith Hospital, also predicted that in 20 years cancer would probably be a chronic but controllable disease. This would mean that the condition would be managed through treatment rather than being seen as an automatic death sentence.
Professor Sikora said that cancer prevention could become more targeted, with a blood test to reveal a person's genetic background and identify any genes that increase the risk of cancer. It meant people might be more motivated to take action to prevent the disease, such as by stopping smoking or losing weight, he told a conference in London.
Ways to cut your cancer risk
* Don't smoke
* Drink less alcohol
* Eat more fruit and vegetables
* Lose weight
* Get more exercise
* Practise safe sex
* Avoid polluted areas
* Don't heat your house with solid fuel
* Avoid injections with dirty needles
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