Global rates of cancer could rise 50 percent, to 15 million new cases a year by 2020, but one-third can be cured and one-third prevented by curbing infections and through lifestyle changes, experts said today.

Once considered a "Western" disease, cancer now affects and kills more people in the developing world than in industrialized nations. In many countries it accounts for more than one-quarter of all deaths.

But according to the World Cancer Report, a comprehensive review of the disease, with existing knowledge it is possible to prevent at least one-third of the 10 million cases that occur each year throughout the world.

"By 2020, there will be a 50 percent increase in the number of people diagnosed with cancer unless steps are taken now," said Bernard W. Stewart, a co-editor of the report.

"The overall message is that we can prevent a third of cancers, we can probably cure a third of cancers and for the remainder we can certainly do something for quality of life if pain management is adequate," he told a news conference.

The report by the International Agency for Research on Cancer, which is part of the World Health Organization, calls for action to stem smoking, improve diet and physical activity and to prevent infections, to curb the disease that kills 6 million people worldwide each year.

Tobacco consumption is the most important avoidable cancer risk worldwide. An estimated 100 million people died of tobacco-related diseases in the 20th century, the report said.

Smokers have a 20 to 30 times greater risk of lung cancer and more likelihood of developing bladder, renal, stomach, liver, kidney and oral cavity cancers, it added.

Health experts predict the biggest reduction in cancer deaths in the coming decades will be due to curbing smoking. But the report says changes in diet -- eating more fruits and vegetables -- increasing exercise and preventing infections such as the hepatitis B and C viruses and other infections linked to liver, cervical and stomach cancers, will also make inroads.

"We know that there is a growing body of evidence on the effectiveness of those interventions," said WHO's Rafael Bengoa.

National screening programs to detect the disease early before it has spread to other parts of the body have produced spectacular results.

Bengoa emphasized the need for better detection and screening in the developing world because 80 percent of cancer patients have incurable tumors when they are diagnosed. Up to 23 percent of cancers in the poor nations are caused by infections, compared with about 8 percent in wealthier countries, so vaccinations could be a key preventive tool.

Vaccination has been shown to prevent stomach cancer in high-incidence countries. Researchers hope to have a vaccine to prevent cervical cancer in three to five years, the report said.

Access to chemotherapy and palliative drugs is another problem in poor countries, where treatments only reach the rich who can afford them. Bengoa said he would like to see differential pricing for expensive cancer drugs.