Cancer rates could fall drastically if efforts to tackle the disease are centred on associated infections, according to experts.

Targeting viruses, bacteria and parasites responsible for triggering cancers could reduce the number of cases by as much as 20%, the World Summit Against Cancer was told.

Dr Harold zur Hausen, of the German Cancer Research Centre in Heidelberg, said tackling viruses was particularly important.

Liver cancer is strongly associated with Hepatitis B and human papillomavirus (HPV) is present in up to 99% of cervical cancer cases.

Brain tumours and childhood leukaemia may also involve viruses.

Dr zur Hausen said: "Global vaccination against Hepatitis B and HPV could theoretically prevent 15% of cancers in females and 10% in males."

'Extremely promising'

Vaccines using particles of HPV virus were being tested in human clinical trials and looked "extremely promising", he said.

Tests are available for HPV, which could be used either in addition to the current smear test used to detect cervical cancer, or on their own. But the test is not currently available on the NHS.

Other scientists are testing vaccines which could prevent the infection.

The conference in Paris also heard that lung cancer is now the leading cause of deaths from any cancer in the world and that this is mostly due to smoking.

Professor Virginia Ernster, of the University of California in San Francisco, who has campaigned against tobacco in the US, said lung cancer was now responsible for one-in-three cancer deaths in men in the US.

She added: "Lung cancer is the leading cause of cancer deaths in the world, and the single most important thing we can do to reduce the cancer burden world-wide would be to dramatically reduce the prevalence of tobacco smoking."

She warned of a potential "epidemic" of tobacco related diseases in the Western world.