'Greater risks from passive smoking - and extra cancers'

Scientists issued the first global warning yesterday that passive smoking causes cancer. They also said that active smokers ran a much greater risk of contracting malignant tumours than previously thought.

Non-smokers who live with smokers are at a 20-30 per cent increased risk of developing cancer, particularly lung cancer, because they are exposed to carcinogenic smoke, research for the World Health Organisation (WHO) showed.

The findings showed that cancers of the stomach, liver, kidneys and cervix as well as myeloid leukaemia can all be caused by smoking, in addition to lung, throat and mouth cancers. The five new cancers on the list of those that can be triggered by smoking means that cigarettes are responsible for hundreds of thousands more deaths each year.

The findings will increase pressure on governments to support tougher restrictions on smoking in public places.

A group of 29 scientists from the International Agency for Research on Cancer (IARC), which is part of the WHO, reviewed more than 3,000 scientific papers on smoking, including 50 large studies on passive smoking. Professor Sir Richard Doll, a member of the group, said it was the first time an international body had given a definitive statement that passive smoking is carcinogenic. "This is the first time there has been a formal evaluation by scientists that has concluded that involuntary smoking causes lung cancer," he said.

The study showed that the dangers of smoking were more serious than previously recognised. Half of adults who persist in smoking will be killed by tobacco-related disease, whether from cancers, heart disease or lung damage. Of these deaths, half will occur in middle age (from 35 to 69 years) and reduce life expectancy by as much as 20 to 25 years, the research showed.

The trend for teenagers to start smoking at younger ages puts them at even greater risk, with some reaching the age of 40 having been committed smokers for 30 years. That pattern will be confirmed in Britain today with new research showing that 10 per cent of children aged 11 to 15 smoke regularly.

The IARC study found that in America and Britain, roughly 90 per cent of lung cancers were attributable to cigarette smoking. But tobacco smoking did not cause all cancers.

The study found little or no evidence to link smoking to breast, endometrial or prostate cancers, which Sir Richard said appeared to be caused principally by hormones.

The IARC team drew no conclusion on whether children who lived with smokers were at an increased risk of cancer because of lack of data. But the chance of a link has not been ruled out.

Tobacco smoke contains more than 4000 chemicals, in the form of particles or toxic gases, which can be directly inhaled or inhaled as sidestream smoke.

With regard to the five new cancers, the scientists said that the toxins could penetrate major organs and cause cells to mutate. Benzene, for example, which is found in tobacco, is a known cause of leukaemia.

Sir Richard said: "I would have personally been resistant to the idea that smoking increases the risk of cancer of the cervix, but the evidence is now compelling. We know that in smokers there are many more mutagenic chemicals than non-smokers."

More than 120,000 people in Britain die each year from smoking-related diseases.