A third of common cancers could be prevented if people stayed focused on a sounder diet, regular exercise and controlled their weight, researchers said on Thursday.
The report, by the World Cancer Research Fund and the American Institute for Cancer Research, analysed incidence of 12 types of cancer in the United States, Britain, Brazil and China.
Around a third of these cancers could be prevented by better nutrition, physical activity and obesity controls, it estimated.
The figure does not include the benefits of tackling cancer by stopping smoking. Tobacco use alone accounts for about a third of cancers.
"On a global level every year, there are millions of cancer cases and this is why we need to act now before the situation gets even worse," said the report's leader, Martin Wiseman.
"We are expecting a substantial increase in cancer rates, with the ageing population, obesity rates soaring, and with people becoming less active and increasingly consuming highly-processed and energy-dense food and drinks.
"The good news is that this is not inevitable and we still have the chance to avert a crisis before it is too late."
The report, Policy and Action for Cancer Prevention, makes four dozen recommendations, authored by 23 leading cancer experts.
It includes the advice that schools and workplaces bar unhealthy foods from vending machines and governments encourage cycling paths and walking routes to promote physical exercise.
According to a report issued on February 2 by health foundation and consultancy Axios International, 12 million new cases of cancer were diagnosed worldwide in 2008, resulting in 7.6 million deaths.
There could be 20 million new cases of cancer each year, and 13 million deaths, by 2030, it estimated.