Passive smoking may speed cancer growth

Second-hand fumes boost blood-vessel development.
23 September 2003

3,000 deaths are attributed to passive smoking
each year.

© GettyImages

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.

The campaign against second-hand smoke took a blow in May, when the British Medical Journal published a study of 35,000 non-smokers married to regular users, which suggested that passive smoking is not a killer². The British Medical Association, which publishes the journal, has since admitted that the research was flawed.

Smoke screen

People with cancer might need to avoid passive smoking

Adrian Harris
University of Oxford

Fume quantities in the mouse study were akin to a human sitting in a car with four smokers lighting up hourly. "The levels were massive," says Harris. He reckons that the mice may therefore be a model of active, rather than passive, smoking. It could imply that nicotine may cause addiction and speed tumour growth in smokers, he speculates.

Tumour growth declined by two-thirds when smoke-doused mice were given drugs that disrupt nicotine or VEGF. The result hints that such drugs could prevent tumour re-growth after radio- or chemotherapy, says Harris.

References

Zhu, B. et al. Second hand smoke stimulates tumor angiogenesis and growth. Cancer Cell, 4, 191 - 196, (2003).

Enstrom, J. E. & Kabat, G. C. Environmental tobacco smoke and tobacco related mortality in a prospective study of Californians 1960-98. British Medical Journal, 326, 1057 - 1061, (2003). |Article|