SINGAPORE - The number of cancer cases in Asia is set to rise dramatically by 2020 due largely to longer life spans and changing lifestyles, threatening a health crisis as poorer countries in the region struggle to afford care.

A fast-growing population coupled with people living longer and undergoing extreme changes to diet and lifestyle will place a major burden on developing countries that cannot afford screening, vaccines and expensive treatment, experts said at the start of a two-day conference in Singapore.

"Many believe that cancer is somehow only a problem of affluent and aging societies. That's not true, of course," said Richard Horton editor and publisher of The Lancet medical journal, which is sponsoring the conference.

Others believe "cancer is somehow inevitable, that one is predisposed to it genetically. Again, that's not true. Forty percent of cancers can be prevented by simple changes in lifestyle."

Cancer of the lungs, stomach and liver are the biggest problems in Asia followed by breast and colon cancers. The total number of new cancer cases in the region is projected to balloon from 4.5 million in 2002 to 7.1 million in 2020 if nothing changes.

"This will put a tremendous burden on patients, their families and the health care system in each country," said Singapore Health Minister Khaw Boon Wan. "Singapore will not be spared. Cancer is already our top killer and we are bracing ourselves for the disease burden to increase as our population ages."

Lung cancer is the biggest problem in Asia, with 600,000 new cases reported annually. Smoking is considered a major contributor.

In several Asian nations, more than 60 percent of the male population smokes, said Dr. Donald Max Parkin, a research fellow at the University of Oxford's Clinical Trial Service Unit and Epidemiological Studies Unit.

"Asia is the epicenter of the smoking epidemic at the moment," Parkin said.

Stomach cancer is also on the rise in Asia, but the risk can be greatly reduced by regular exercise and having a healthy diet that's low in salt and fatty foods.

Large populations of Asians have moved from the countryside to cities where their lives have become more sedentary and their eating habits have changed, with people consuming less vegetables and more meat and fried foods.

Preventing hepatitis B through vaccination also helps lower the chances of developing liver cancer, also a major problem for the region, Parkin said.

Worldwide, there are 11 million new cancer cases reported annually and 7 million people die from the disease each year, according to the International Agency for Research on Cancer.