Can nicotine gum cause mouth cancer?

For people who want to stop smoking, there are many different options available. These include products based on nicotine, the addictive drug that keeps smokers hooked.

These “nicotine replacement therapies” or NRT can take the form of gum, patches, nasal sprays or tablets. In each case, they aim to help smokers wean themselves off tobacco by providing a hit of nicotine without any of the other cancer-causing substances found in cigarette smoke. NRT products work by giving less nicotine more slowly and are much less addictive.

This week, alarming headlines hit the newspapers claiming that the nicotine in these products could actually cause mouth cancer. But while the results are interesting, this conclusion and many of the news stories based on it are premature.

The study was published in the journal PLoS ONE. It looked at one specific gene – FOXM1 – and the protein that it encodes. FOXM1 is a “transcription factor”, a master protein that can switch other genes on or off. It’s often overactive in various cancers.

The researchers looked at samples of mouth cells grown in the lab and taken from 75 people, of whom 15 had mouth cancer. They found that high levels of FOXM1 activity were associated with mouth cancer. Compared to normal mouth cells, the gene was more active in those that were on the verge of becoming cancerous, and even more active in those that had actually turned into cancer cells.

The researchers then exposed the lab-grown mouth cells to concentrations of nicotine, similar to those that build up in the mouths of people who chew nicotine gum. They found that at these concentrations, nicotine switched on the FOXM1 gene in their cells, and speeded up the transformation of normal cells into cancerous ones.

That’s a surprise – there are around 70 cancer-causing substances (carcinogens) in tobacco products, but most scientists feel that nicotine isn’t one of them. It’s obviously very addictive and at high doses, it can be very poisonous, but it’s not regarded as a cause cancer.

Some studies have suggested that it could influence the growth of cancerous cells, but even that is controversial. Whatever the situation, it’s clear that the nicotine itself is either harmless or substantially less harmful than the full gamut of chemicals in tobacco smoke.

The researcher themselves say: “We’ve showed the FOXM1 gene is activated by nicotine in human mouth cells which raises the possibility that nicotine could potentially increase the risk of mouth cancer. We want to stress, however, that further research is needed to conclusively determine whether this is indeed the case. There is no doubt however about the harmful effects of smoking, so smokers should make every effort to quit.”

Caution needed

The research team are right to advise caution. While their results are interesting and based on sound science, we have to remember that the study was done in a relatively small number of cell samples that had been grown in the lab.

Experiments like this can raise questions that prompt further research but alone, they can’t be treated as convincing evidence that something causes cancer. Often, laboratory studies have reported that a certain chemical increases or reduces the risk of cancer, only for larger studies in actual people to contradict those results (take the case of vitamin supplements, as an example).

This view was echoed by Professor Robert West, Director of Tobacco Studies at Cancer Research UK’s Health Behaviour Research Centre, who has done a lot of work looking into NRT. He said:

“The interpretation is highly speculative and contradicted by evidence that many millions of people have been using nicotine replacement therapy with no increased risk of oral or any other cancer. If reports like this stop people using what for many would be a life-saving medication it would be very unfortunate.”

Professor West is certainly right that nicotine replacement therapy can save lives. Smoking is the single biggest cause of cancer in the UK, and indeed, it’s the main cause of mouth cancer.

Because of cancer, heart disease, stroke and other conditions, the average smoker loses 10 years of their life. Helping more people to become non-smokers is the single best thing we can do to reduce the number of people who develop cancer. And as a way of helping people to quit smoking, nicotine replacement therapy works.

In 2007, the Cochrane Collaboration reviewed 132 trials using NRT. It concluded that “all of the commercially available forms of NRT (gum, transdermal patch, nasal spray, inhaler and sublingual tablets/lozenges) can help people who make a quit attempt to increase their chances of successfully stopping smoking.” The best of these products managed to double the chances of quitting successfully. They even work if smokers receive no extra support from other sources.

For a smoker, the health hazards of continuing to smoke greatly outweigh any potential risks of using NRT – and of course, the latter can help you to quit. Dr Muy-Tech Teh, who led the new research, agrees. “Smoking is of course far more dangerous, and people who are using nicotine replacement to give up should continue to use it and consult their GPs if they are concerned. The important message is not to overuse it, and to follow advice on the packet.”

Ed