Researchers have found that that nicotine, a non-carcinogenic chemical found in tobacco, actually promotes the spread of lung cancer cells into the brain where they can form deadly metastatic tumours.

For our comprehensive coverage and latest updates on COVID-19 click here.

Smokers are far more likely to develop lung cancer than non-smokers, the study said. "Based on our findings, we don't think that nicotine replacement products are the safest way for people with lung cancer to stop smoking," said study lead author Kounosuke Watabe from Wake Forest School of Medicine in the US. Around 40 percent of lung cancer patients also develop brain metastasis, but new research has found this number is dramatically higher among smokers.

In the study, published in the Journal of Experimental Medicine, the research team first examined 281 lung cancer patients and found that cigarette smokers exhibited a significantly higher incidence of brain cancer. Then, using a mouse model, the researchers discovered that nicotine enhanced brain metastasis by crossing the blood-brain barrier to change the microglia - a type of immune cell in the brain - from being protective to supporting tumour growth. The team then looked for drugs that might reverse the effects of nicotine and identified parthenolide, a naturally occurring substance in the medicinal herb feverfew, which blocked nicotine-induced brain metastasis in the mice. Because feverfew has been used for years and is considered safe, the researchers believe parthenolide may provide a new approach to fight brain metastasis, particularly for patients who have smoked or still smoke.

"Currently, the only treatment for this devastating illness is radiation therapy," Watabe said. "Traditional chemotherapy drugs can't cross the blood-brain barrier, but parthenolide can, and thus holds promise as a treatment or possibly even a way to prevent brain metastasis," Watabe added.