Passive smoking may speed the growth of tumours by prompting new blood vessels to form, a new study suggests1. The finding strengthens the link between second-hand tobacco fumes and lung cancer, and could aid the development of therapies for tobacco-related diseases.
People who regularly inhale others' smoke - those who live with smokers or work in smoky bars and restaurants - have a 20-30% greater risk of contracting lung cancer or heart disease. In the United States alone, 3,000 deaths are attributed to passive smoking each year.
Cigarette fumes contain more than 60 chemicals, including arsenic and benzene, that encourage tumours. "Passive smoking accelerates the growth of pre-existing tumours," says John Cooke of Stanford University School of Medicine in California.
Cooke's team injected mice with lung-cancer cells and then exposed them to second-hand smoke or clean air for 17 days. Both groups developed tumours, but in the fume-breathing mice the growths were up to five times larger and were fed by elaborate blood supplies.
These animals had twice as much VEGF - a molecule that stimulates blood vessels to grow - as their clean-air counterparts.
"It means that people with cancer might need to avoid passive smoking," says Adrian Harris of the University of Oxford, UK, who studies tumour growth.
Lighting up in bars and restaurants is already illegal in many US cities, including New York. A proposed European Union ban on smoking in public places is currently under discussion. "The research is important medically and socially," says vascular biologist Peter Carmeliet of the Catholic University of Leuven in Belgium.
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