Tobacco and Cancer

What kinds of cancer does tobacco cause in smokers?

Nearly 20 years ago, the International Agency for Research on Cancer (IARC) reported that tobacco smoking increased risks of cancers of the lung, oral cavity (mouth), pharynx, larynx, oesophagus (squamous-cell carcinoma), pancreas, bladder and renal pelvis (the kidney outlet). Smokers are much more likely to develop these cancers than non-smokers: between 3 times more for pancreas cancer and 20 times more for lung cancer.

It is now established that tobacco smoking also increases by about 2 to 3 times the risk of getting cancers of the nasal cavities (nose), nasal sinuses, oesophagus (adenocarcinoma), stomach, liver, kidney and cervix (neck of the uterus) and developing myeloid leukaemia

Which cancers are caused by cigarette smoking?

2.1.1 Lung: Lung cancer is the most common cause of cancer deaths in the world and 1.2 million people develop it each year. In populations where tobacco has been widely used for a long-time (e.g. among men in developed countries) smoking is responsible for 90% of the cases of lung cancer. The risk of lung cancer increases in proportion to the duration of smoking and the numbers of cigarettes smoked. The effects are similar in men and women.

Stopping smoking at any age avoids further increasing the risk of lung cancer. The younger the age at which a person quits, the greater is the benefit.

2.1.2 Urinary tract: Tobacco smoking is a major cause of several cancers of the urinary tract (bladder, ureter and kidneys). The risk depends on duration of smoking and number of cigarettes smoked. As for lung cancer, stopping smoking at any age avoids further increasing the risk.

.2.1.3 Oral cavity (mouth): Tobacco smoking causes cancer of the oral cavity in men and women. The risk is increased when smokeless tobacco is used or when smoking is combined with alcohol consumption. There is a strong relationship between risk and duration of smoking and number of cigarettes smoked. The risk tends to decrease after quitting.

2.1.4 Nasal cavity (nose) and paranasal sinuses: Sinonasalcancer is increased among cigarette smokers and several studies have shown that its frequency increases with the amount smoked.

.2.1.5 Pharynx (nasopharynx, oropharynx and hypopharynx): The risk of cancer in the pharynx increases with cigarette smoking, depending on duration and number of cigarettes smoked. The risk decreases with time after quitting.

2.1.6 Oesophagus: Tobacco smoking increases the risk of oesophageal cancer in relation to dose. Stopping smoking does not result in a rapid decline in this risk. The risk is increased when smokeless tobacco is used or when smoking is combined with alcohol consumption.

2.1.7 Larynx: Laryngealcancer is causally related with cigarette smoking with the risk increasing with dose. Use of alcohol in smokers and early age at starting smoking increase the risk. More...

2.1.8 Pancreas: Cigarette smoking causes cancer of the pancreas in proportion to consumption

2.1.9 Stomach: Many studies have now provided evidence of the role of cigarette smoking in causing stomach tumours, after allowing for other confounding factors. The risk is proportional to the duration of smoking and number of cigarettes smoked.

2.1.10 Liver: Many recent studies have now shown that cigarette smoking gives a moderate increased risk of liver cancer, in relation to the duration of smoking and the number of cigarettes smoked.

2.1.11 Cervix (neck of the uterus): A large number of studies have demonstrated that smoking induces one type of cervical cancer but the evidence is not consistent for other cervical carcinomas.

2.1.12 Bone marrow (leukaemia): Adult myeloid leukaemia is causally related to smoking. No clear evidence has been found for a link with lymphoid leukaemia or lymphoma. More...

What other biological effects can active smoking cause?

Active smoking causes adverse reproductive outcomes and various health effects other than tumours, including respiratory and cardiovascular diseases.

Nicotine is the major addictive component of tobacco. In the human body, it is transformed into the metabolite cotinine, which is used as a reference to indicate exposure to tobacco smoke since it is found only in smokers and in passive smokers (in blood, urine and saliva).

Air exhaled by smokers contains higher concentrations of the following chemicals: carbon monoxide, benzene and volatile organiccompounds. Moreover, some important carcinogens present in tobacco smoke and their metabolites are found in the urine of smokers.

Carcinogens present in tobacco smoke can react with proteins and DNA to form "adducts". Such carcinogen adducts are present in many tissues of smokers at higher levels than in non-smokers, for instance in the respiratory tract, bladder and cervix (neck of the uterus). Some but not all studies have also found adducts in the umbilical cord blood of smoking mothers and in cardiovascular tissues. Adducts can damage cells by producing gene mutations and chromosomal abnormalities.

Smoking can alter the activity of many enzymes involved in normal body metabolism.

In humans, smoking produces gene mutations and chromosomal abnormalities. Urine from smokers is mutagenic. Relative to non-smokers, lung tumours of smokers have unique features specific to exposure to tobacco smoke. Tobacco smoke is genotoxic in humans and in test animals.

In test animals, exposure to tobacco smoke also alters a variety of enzyme activities, results in formation of DNAadducts in several tissues and alters lung function.

What is passive smoking?

Passive smoking is involuntary exposure to tobacco smoke. The secondhand smoke inhaled by passive smokers is a mixture of smoke exhaled by smokers and smoke directly released from smouldering tobacco. It contains nicotine as well as various carcinogens and toxins.

Does passive smoking cause cancer?

6.1 There is sufficient evidence to conclude that there is an increased risk of lung cancer for people who have never smoked but who have been exposed to tobacco smoke, e.g. spouses of smokers and non-smokers exposed at the workplace. However, the risk is much smaller than for active smokers. More...

6.2 For other cancers such as breast and childhood cancer, however, evidence is not conclusive. More...

6.3 Studies on laboratory animals support the evidence that passive smoking can cause cancer in humans and there is some data suggesting that dogs living in smoking households also have an increased risk for certain cancers.

Does passive smoking cause other health effects?

7.1 Passive smoking can cause coronary heart disease and chronic respiratory symptoms.

7.2 Though passive smoking does not seem to affect body weight, fertility and age at menopause of women, the birth weight of babies born to passive smokers may be lower than those born to non-smokers.

7.3 Similar to active smokers, passive smokers have harmful substances and breakdown products of tobacco smoke in their body, which can cause cell damage and lung cancer.

7.4 Test animals exposed to secondhand tobacco smoke show a range of adverse effects, including DNA damage, altered metabolism, reduced birth weight, as well as diseases of the arteries and the respiratory system

Conclusions on tobacco and cancer

8.1 There is sufficient evidence to conclude that tobacco smoking causes several types of cancer in humans.

8.2 Moreover, there is sufficient evidence to conclude that passive smoking causes lung cancer in humans.

The International Agency for Research on Cancer (IARC) has therefore classified both active and passive tobacco smoking and tobacco smoke as "carcinogenic to human

Sunbeds & UV radiation

What are the health effects of solar UV radiation?

The risk of skin cancer depends on skin type
Credit: Dr A.R. Young

2.1 Exposure to sunlight has some beneficial effects. It is responsible for the production of vitamin D in the body, which is essential for maintaining healthy muscles and bones and may also have other health benefits. However, eating foods rich in vitamin D or taking adequate levels of vitamin D supplements is likely to produce the same beneficial effects. More...

2.2 In the short term after exposure, UV radiation can cause sunburn, aggravate certain skin diseases, and affect the immune system. It can also cause adverse reactions in people who take certain medicines or those who apply creams or other products containing particular chemicals.

UV radiation can harm the eyes

In the long term, exposure to UV radiation can cause skin cancers and premature ageing of the skin. The risk of developing skin cancers depends on the amount and pattern of sun exposure, and on skin type. For the most lethal type of skin cancer, the risk also depends on age, physical characteristics such as fair hair or the presence of moles and freckles, as well as family history of skin cancer. More...

2.3 UV radiation can also harm the eyes. In the short term, it can cause a kind of "eye sunburn", a temporary but painful inflammation of the outermost layer of the eye.

In the long-term, it can increase the risk of developing several eye diseases, including cataracts and eye cancer.