The link between smoking and cancer

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Tobacco smoking is the single largest extrinsic risk factor for cancer in developed countries, causing almost one in five cases of cancer and 28% of cancer-related deaths in the UK in 2005. Worldwide, smoking causes more cancer deaths than all other known risk factors, and causes even more deaths from vascular and respiratory diseases than from cancer.

The most common cancers worldwide are those of the lung, breast and colorectum, while the most common causes of cancer-related death are lung, stomach and liver cancers. Lung cancer is thus of particular concern as not only is it one of the most common cancers, it is also one of the most common causes of cancer death. It was reliably established in the 1950s that the major cause of lung cancer is smoking tobacco, particularly cigarettes, with more than 4 in 5 lung cancer cases in the UK being caused by smoking. Smoking also increases the risk of at least 13 other cancers, including: larynx (voice box), oesophagus, mouth and pharynx (upper throat), bladder, pancreas, kidney, liver, stomach, bowel, cervix, ovary, nose and sinus, as well as some types of leukaemia. In the past few decades, it has also been increasingly clear that there is also cancer risk from second-hand smoking.

Cumulative risk of death from lung cancer in men at ages 45-75 years
Cumulative risk (%) of death from lung cancer (in the absence of other causes of death) in men at ages 45-75 years: in continuing cigarette smokers, ex-cigarette smokers who stopped at age 50 or age 30 and lifelong nonsmokers, based on lung cancer death rates for men in the United Kingdom in 1990. Taken from: Peto, R., Darby, S., Deo, H., Silcocks, P., Whitley, E. & Doll, R., 2000. Smoking, smoking cessation and lung cancer in the US since 1950: Combination of national statistics with two case-control studies. Br. Med. J., 321, pp.323-329.

Tobacco consumption was originally popularised in America, then in Europe in the 16th and 17th centuries, and subsequently globally. Cigarettes, which became the most common method of smoking tobacco in the 20th century, have been shown to be significantly more dangerous than the pipe or cigar smoking common in the 19th century. The spread of cigarette smoking in some countries during the 20th century was driven by tobacco companies themselves.

More recently, major efforts have been made in some countries to discourage smoking to some success - for example, cigarette consumption has been halved in a few countries (including the USA, the UK, Canada and France) over the past few decades. However, consumption has increased rapidly in many developing countries, and over one billion people currently smoke worldwide, with 30 million young adults taking up the habit each year. The emergence of increasingly large multinational tobacco companies with global reach could lead to even greater consumption in the future.

Based on current smoking patterns, smoking is expected to cause about 150 million deaths in the first quarter of the 21st century, and 300 million in the second quarter. Thus, helping large numbers of smokers to quit and many young adults not to start smoking in the first place in the next couple of decades could avoid hundreds of millions of smoking-related deaths.

Projected numbers of death from smoking in 21st century.
Projected numbers of deaths from tobacco smoking during the twenty-first century. Taken from: Prabhat, J., 2009. Avoidable global cancer deaths and total deaths from smoking. Nature Reviews Cancer, 9, pp.655-664.

At the 13th CR@B Symposium on 27th April, Dr Jenny Hatchard, Research Associate in the Department for Health at University of Bath, spoke about how tobacco companies are the vector of smoking-related cancers.

Other topics that will be covered by speakers from several different universities and RUH Bath include: integration of approaches in behavioural science and cancer research, synthesis of multimodal PET and SPECT imaging agents towards hypoxia-selective inhibitors, symptom appraisal of pain and cancer survival, and the influence of tumour microenvironment on drug response and targeting tumour stroma.

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