Smoking could speed up the growth of lung cancers as well as causing them in the first place, researchers have claimed.

It is known that smoking and passive smoking cause nine out of 10 lung cancers because carcinogens in the smoke trigger pre-cancerous mutations in DNA. But researchers from the US suggest nicotine could make lung cancers more aggressive by stimulating tumour cells to grow and divide. Research was carried out in patients with small cell lung cancer. It was discovered that some tumour cells are primed to respond to a chemical called acetylcholine. These receptors are known to be activated by nicotine. Tumour cells also made large amounts of the acetylcholine. Scientists had previously only thought it acted as a neurotransmitter. But the researchers from the Oregon National Primate Research Center in Beaverton suggest acetylcholine may also act as a growth factor outside the nervous system. In tumours, they suggested this could mean acetylcholine fuelled the continuous growth and division of cells. Drug treatments They decided to see if blocking acetylcholine receptors could halt tumour growth. Cells were treated with atropine, which blocks acetylcholine receptors, and tumours stopped growing. Eliot Spindel, who led the research, told New Scientist magazine: "Our discovery reveals the little extra push by nicotine." He said it could be possible to adapt substances such as atropine into drugs which could be used to treat lung cancer. "You must find the right dose, or a pathway unique to lung cancer that doesn't affect the nervous system." But he added: "This loop can be revved up by smoking so there's no question that not smoking is the best thing you can do." Marcus Munafo, a Cancer Research UK expert at the Institute of Health Sciences in Oxford agreed, but added: "In the light of the new findings, it would be worth looking into whether or not stopping smoking makes a difference to survival rates in people already diagnosed with lung cancer."

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