For a long time, it has been known that smoking significantly increases the chances of developing cancer. Yet despite this knowledge, smoking-related cancers still account for around a fifth of all UK cancer cases, making smoking the biggest preventable cause of cancer.
Tumours form due to mutations within cell DNA that allow cells to divide uncontrollably. For a tumour to become cancerous through further mutations, cells must also gain the ability to metastasise (spread to other parts of the body) and develop other traits which are known as the ‘hallmarks of cancer’. There were originally six hallmarks of cancer cells, but in 2011 this number was updated to ten:
The ten hallmarks of cancer (Hallmarks of Cancer: The Next Generation – Hanahan & Weinberg, 2011, http://dx.doi.org/10.1016/j.cell.2011.02.013)
Not every individual cancer cell will have all the hallmarks of cancer. It is likely that within a tumour, sub-populations of cancer cells will exist with different mutations, and therefore different hallmarks. The presence of cells with different mutations within a tumour is the reason that treating cancer can be so difficult.
Mutations occur naturally at a very low rate when DNA is copied to form new cells that replace dead cells. Research has found that smoking one pack of cigarettes a day can cause an additional 150 mutations in lung cells every year. Therefore, smoking significantly increases the risk of cells becoming cancerous.
Smoking causes mutations to arise due to oncogenic (cancer-causing) chemicals found within cigarettes. It is believed that out of the 250 known harmful chemicals in cigarettes at least 69 of these cause DNA damage, and consequently cancer-causing mutations.
The chemicals from cigarettes are absorbed into the bloodstream and transported around the body. This is how smoking causes not only mouth and lung cancers, but 12 other known cancers: including pancreatic, stomach, ovarian and liver cancers.
Strong evidence that smoking is the direct cause of tumours in multiple areas of the body came from collaborative research done at a number of centres, including the Wellcome Trust Sanger Institute. The research identified a mutational signature (a pattern of mutations) unique to the tumour cells of smokers.
They did so by comparing the mutations in tumour cells of smokers to the mutations found in tumour cells of non-smokers. The researchers identified mutational signatures, not only in lung cancer cells, but also in the tumour cells of mouth, bladder, liver, larynx and pharynx cancers.
The cancer risk associated with smoking was first suggested during the 1940/50s, due to a global epidemic of lung cancer following a marked increase in smoking uptake during the late 19th and early 20th century. Despite this, in the 1960’s only a third of US doctors believed that there was sufficient evidence to confirm the link between smoking and lung cancer.
Since this, the link has become widely accepted and despite tobacco company’s best efforts to glamorise smoking, rates of smoking in the UK have seen a marked decrease in the last few decades. In 2014, 19% of the UK population smoked, with slightly higher rates in men than women. This was a dramatic decrease from nearly half of the population 40 years prior.
The average number of cigarettes consumed has also fallen from around 16 cigarettes to more like ten cigarettes per day. The UK lifestyle survey suggests that smoking prevalence is greatest in young adults between the ages of 20 and 24 years old, whereas previously rates were highest in people aged between 25 and 59 years of age.
The changes seen in smoking rates in the UK between 1974 and 2014 are likely due to several initiatives and rulings implemented to reduce smoking, including:
▪ The prohibition of tobacco advertising on TV and radio in the broadcasting acts of 1990 and 1996
▪ The total ban on advertising and tobacco company event sponsorship in the UK in 2003
▪ The global ban on event sponsorship in 2005.
▪ The 2007 ban of smoking in enclosed public place – the biggest change in the UK but one that very few EU countries have implemented.
Since 2014, campaigning by Cancer Research UK (CRUK) and Action on Smoking and Health (ASH) has seen the introduction of further legislation that attempts to prevent people taking up smoking by making it less appealing.
The changes include the ban on displaying cigarette sales, and the ban on branding tobacco products – meaning only plain, standardised cigarette packaging is allowed. The UK is the second country to introduce laws that allow only this packaging and the decision was based upon the successful impact the same law had had on reducing smoking rates in Australia.
CRUK states that people using stop smoking services have a greater success rate when attempting to quit smoking compared to those who try alone. The Smokefree service from the NHS provides free text, email and face-to-face support, as well as an initial Quit kit and an app to help people quit smoking.