Does nicotine cause cancer?

Every now and again we see a new newspaper headline claiming that nicotine causes some serious health problem, whether it be heart attacks or cancer. Usually the headline is based on a very small study in humans, or a laboratory study of cells in a petri dish or test tube. In the past week we saw the latest example. A study by Gemenetzidis and colleagues in London examined the effect of nicotine on a protein transcription factor named FOX-1 in tissue cells in the laboratory. Fox-1 expression has been associated with onset of tumor growth in prior studies. The study found that nicotine application to cells in the lab resulted in an increase in Fox-1 expression (in the laboratory, not in humans). The authors therefore concluded that nicotine , by stimulating FOX-1 expression, may promote cell instability and tumor growth.

The thing that is relatively new about this finding is that many prior studies and reviews have concluded that nicotine does not play a part in stimulating tumor development or growth. So for this study to claim that nicotine causes cancer is contrary to previous expert opinion.

I am not a cell biologist and cannot claim to fully understand the science contained in this recent publication by Gemenetzidis and colleagues. However, I can think of some ways of assessing whether the laboratory finding really does translate into health effects in the real world. In many countries around the world people use smokeless oral tobacco for most of their adult life. Oral smokeless tobacco delivers high quantities of nicotine (in addition to other proven carcinogens), but without delivering any smoke. In Sweden there is a tradition of men using a form of smokeless tobacco, called snus, that is relatively low in other toxins. So if nicotine really does have a role in increasing oral cancer risk, we would assume that people using this nicotine delivery product throughout their whole life would have an increased oral cancer risk. However, numerous long term epidemiological studies of Swedish men who use this oral tobacco product have found that they do not have an increased rate of oral cancer, as compared with men who never used any tobacco products.

Gemenetzidis and colleagues, on the basis of their lab study of cells in the lab, have cautioned against the use of nicotine replacement therapy in case it causes cancer. Now nicotine replacement therapy is typically used for up to 12 weeks, but occasionally for longer. But NRT typically delivers lower levels of nicotine than snus smokeless tobacco and is almost never used in a lifelong fashion ….daily from teenage years for life, as is common for smokeless tobacco. So to my way of reading the epidemiological evidence, if lifelong use of high nicotine oral tobacco does not increase the risk of oral cancer, then the risk that a few months of NRT use will cause oral cancer are non-existent. So no, I don’t believe that this study provides convincing evidence that nicotine causes cancer.

Sometimes I wish that lab scientists would check out the epidemiological evidence before announcing to the press that effective therapies may cause cancer.


Example article last week in the London Times:
http://www.timesonline.co.uk/tol/life_and_style/health/article6143744.ece

The full study report can be viewed at:
http://dx.plos.org/10.1371/journal.pone.0004849

For a very thorough review of the health effects of nicotine, and of smokeless tobacco, check out the relevant chapters of the recent Royal College of Physicians report on tobacco harm reduction at:
http://www.rcplondon.ac.uk/pubs/brochure.aspx?e=234

Labels: cancer, jonathan foulds, nicotine, NRT

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