An international conference on lung cancer opened in Tokyo this week with some 2,500 doctors and researchers expected to adopt a declaration calling for nonsmoking government policies around the world.

Participants in the ninth World Conference on Lung Cancer, scheduled to last until Friday, will discuss the latest methods of treating, diagnosing and preventing lung cancer, organizers said.

They will adopt the antismoking Tokyo Declaration at Thursday's general assembly, calling on governments around the world to introduce policies promoting nonsmoking, because smoking is considered a major cause of lung cancer, the organizers said.

Lung cancer is said to be difficult to treat and has the highest death rate among cancer patients.

The number of men dying from lung cancer has decreased in the United States and parts of Europe where people have curbed smoking.

However, the overall death rate as well as the figures in countries including Japan continue to rise.

"By promoting nonsmoking and measures to deal with diesel exhaust, we want to lower the occurrence of lung cancer and advance early discovery and treatment of the disease," said Harubumi Kato, a professor at Tokyo Medical University.

"This conference is an important place to seek the path toward that end," said Kato, president-elect of the International Association for the Study of Lung Cancer, the sponsor of the conference.