Smoking not only causes cancer, it may also speed up the growth of existing tumours, according to new research.
Scientists at the Oregon National Primate Research Center in Beaverton suggest that nicotine in cigarette smoke could stimulate the production of a molecule that can make lung cancer cells more aggressive and encourages them to divide and grow.
"Smoking may boost the growth of existing tumours as well as triggering cancer," New Scientistmagazine said.
The molecule, called acetylcholine, is a neurotransmitter, or message-carrying chemical, in the brain and nerves. Mr Eliot Spindel and his colleagues found that some cancerous cells have receptors, or molecular doorways into cells, for the molecule.
They also discovered that fast-growing cells make large amounts of the molecule and have a feedback loop so that the acetylcholine they make encourages them to divide and grow.
But when the scientists cut the loop by blocking the receptors with the nerve gas antidote atropine the cells stopped growing.
"Our discovery reveals the little extra push by nicotine," said Mr Spindel, who reported his research in the journal Life Sciences.
He believes it may be possible, though not easy, to adapt drugs such as atropine to treat lung cancer but added that the correct dose and making sure it doesn't affect the nervous system would be crucial.