Lung cancer risk factors

Smoking causes lung cancer, the International Agency for Research on Cancer (IARC) states.2 86% of lung cancers in the UK in 2010 – around 34,600 cases – were caused by tobacco smoke, it has been estimated.3 Exposure to environmental tobacco smoke (ETS) among non-smokers accounted for around 1,000 (3%) of those cases. The total population attributable fraction for tobacco smoke is higher for men (87%) than women (84%), which reflects the higher smoking prevalence among men in the past.3

See our smoking statistics page for details of smoking prevalence in the UK and abroad.

Current smokers are around 15 times more likely than lifelong non-smokers to die from lung cancer, a 50-year-long study of British male doctors shows.4 Those with longer duration of smoking and higher levels of tobacco consumption have higher risks of developing lung cancer,4 but lung cancer risk is more dependent on the duration of smoking than on the level of consumption. Smoking one pack of cigarettes a day for 40 years is more hazardous than smoking two packs a day for 20 years.5-7 Accordingly, starting to smoke at a young age carries additional risks of lung damage.8-10 Female smokers’ risk of dying from lung cancer may increase by more than a third for every five years younger they were when they started smoking.11

Smoking 1-4 cigarettes each day increases the risk of dying from lung cancer by around three times in men and by around five times in women, compared with never-smokers.12 People who smoke 8-12 cigarettes a day have around 12 times the risk of dying from lung cancer, and those who smoke 25 or more cigarettes a day have at least 24 times the risk,4,13 compared with lifelong non-smokers. People who smoke more than two packs a day (42 or more cigarettes) are 39 times more likely to die from lung cancer death compared with never-smokers, a large US study of middle-aged people shows.13 In line with these mortality risk increases, the risk of being diagnosed with lung cancer is also increased, by around 26 times in men who smoke 15-24 cigarettes a day, compared with lifelong non-smokers.14

Stopping smoking

Smoking cessation has very significant health benefits, including improved life expectancy, even for people who have been smoking for many years, or who quit smoking at older ages.9,10,15 But just reducing cigarette intake may not have significant benefits on lung cancer risk: heavy smokers (around 16-18 cigarettes per day) who halved their intake did not significantly reduce their lung cancer risk in comparison with sustained heavy smokers.16

Giving up smoking in middle age avoids most of the subsequent risk of lung cancer. A lifelong male smoker has a cumulative risk of 15.9% for dying from lung cancer by age 75.9 Men who stop smoking by age 60 cut their cumulative risk of lung cancer death to 9.9%.9 The younger men are when they stop smoking, the greater the decrease in their risk of dying from lung cancer: men who stop by age 50, 40 and 30 years have cumulative risks of dying from lung cancer of 6.0%, 3.0% and 1.7% respectively.9

Smoking cessation has similar health benefits for women. A lifelong female smoker has a cumulative risk of dying from lung cancer by age 75 of 9.5%, but for women who stop smoking around age 60 and 50, this cumulative risk falls to 5.3% and 2.2% respectively.9

Similar effects have been observed in other European countries and the US.17-19 Even giving up smoking after lung cancer has been diagnosed can be beneficial – it is estimated to around double five-year survival in 65 year-old patients diagnosed with early-stage non-small cell cancer or limited stage small cell cancer.20

Secondhand smoke

Secondhand tobacco smoke (also called environmental tobacco smoke, ETS) causes lung cancer, IARC states.2 It accounted for an estimated 15% of lung cancer cases in never-smokers in the UK in 2010.3 Exposure to ETS at home or at work among non-smokers increases risk by about a quarter, meta-analyses have shown.21,22 People with the highest workplace ETS exposure levels have double the lung cancer risk.22

It is less clear whether ETS exposure in childhood is associated with increased lung cancer risk in adulthood. Studies published up to 1998 overall found no significant association, a meta-analysis showed.23 Since then, a large cohort study has reported no significant association.24

See the our smoking statistics page for more detailed smoking statistics.

section reviewed 04/01/13
section updated 04/01/13

Radon is a naturally occurring radioactive gas which comes from the minute amounts of uranium that occur naturally in all rocks and soils.25 It is a known human carcinogen, classified as a cause of lung cancer by IARC.2 The association with lung cancer was first observed in uranium miners with high radon exposure levels.26 Occupational exposure to radon through working in sites located in areas of naturally occurring high radon exposure is estimated to have caused around 180 lung cancer deaths in Britain in 2005.27 Radon can also accumulate at much lower levels in homes and other buildings.25 The highest levels of radon in the UK are most widespread in south west England, although similar levels are found in localised areas in many other parts of the UK.25

Around 1,400 lung cancer cases in the UK in 2010 were due to radon in the home, it is estimated.28 However, the majority of these (around 87%) were caused by the combination of radon exposure and smoking, with the remainder in people who had never smoked.28 Exposure to 100 radon becquerels per cubic metre (Bq/m3) is associated with a 16% increase in lung cancer risk.14 The radon level in the average UK home is 20 Bq/m3.25 Indoor radon exposure may be responsible for 9% of lung cancer deaths in European countries, it is estimated.14

The effect of radon exposure on lung cancer risk does not appear to differ between smokers and non-smokers.14 But because smokers’ underlying risk of lung cancer is already much higher, smokers exposed to radon have much higher lung cancer risks than do non-smokers exposed to radon.14

Other sources of ionising radiation

X radiation and gamma radiation are classified as causes of lung cancer by IARC.2 Radiotherapy is estimated to have caused around 320 cases of lung cancer in the UK in 2010. Diagnostic radiation caused around 120 cases, and natural (background) radiation caused around 85 cases, it is estimated.28

section reviewed 04/01/13
section updated 04/01/13

Asbestos exposure is classified as a cause of lung cancer by IARC.2 It accounted for more than 1,900 lung cancer deaths in Britain in 2005, it is estimated.27 People working in construction and shipyards were at particular risk of exposure,31 however exposure in the UK is estimated to have peaked around 1963 and decreased rapidly thereafter.32 Though asbestos is the primary cause of mesothelioma, it is thought to cause as many lung cancer cases as mesothelioma cases, because the former is much more common than the latter.27,33 Exposure to asbestos increases the risk of lung cancer death by 77%, and accounts for at least 8% of lung cancer deaths in total in the UK, it is estimated.33 As current smokers have around 15 times higher risk of lung cancer death than do never-smokers,4 so  asbestos-exposed current smokers have between 19 and 26 times higher risk of lung cancer death compared with asbestos-exposed never-smokers, a large study showed.34 This suggests that smoking and asbestos have a synergistic effect on lung cancer development, meaning that their effect in combination is stronger than the sum of their independent effects.34-37

section reviewed 04/01/13
section updated 04/01/13

Silica dust exposure causes lung cancer, states IARC.2 Around 790 lung cancer deaths in Britain in 2005 are thought to have been linked to silica.27 The primary industrial use for silica is glass manufacture. It appears that silica may induce lung cancer indirectly, by causing silicosis. People with silicosis (silicotics) have around double the risk of lung cancer; but silica exposure in the absence of silicosis does not appear to associated with lung cancer risk;38,39 however, evidence in non-silicotics is inadequate to draw firm conclusions.38

section updated 04/01/13
section updated 04/01/13

Diesel exhaust is classified as a cause of lung cancer by IARC.40 Around 600 lung cancer deaths in Britain in 2005 were linked with occupational exposure to diesel exhaust, it is estimated.27 Evidence for the association between diesel exhaust and lung cancer comes mainly from highly-exposed workers.40 Miners heavily exposed to diesel exhaust have approximately three times higher risk of lung cancer.41 Professional drivers working for at least 10 years have a 19% increased lung cancer risk, probably due to diesel exhaust exposure, a meta-analysis reported.42

section updated 04/01/13
section updated 04/01/13

Exposure to mineral oils is not classified as a cause of lung cancer by IARC,2 but it is estimated to have caused 410 lung cancer deaths in Britain in 2005.27 Mineral oil exposure occurs most commonly among metalworkers and printworkers.

Working as a painter is a cause of lung cancer, IARC states.2 This occupation was linked to around 250 lung cancer deaths in Britain in 2005. Painters may be exposed to solvents in their work, however IARC does not identify specific substances responsible for the risk increase. Painters have a 22-57% increased risk of lung cancer, several meta-analyses have shown.43-45

IARC states that TCDD (2,3,7,8-tetrachlorodibenzo-para-dioxin) may cause lung cancer.2 Around 190 lung cancer deaths in Britain in 2005 were linked to TCDD exposure, it is estimated.27 TCDD exposure may occur in a number of industries, including production of some metals and pesticides. Pesticide production workers have a 22% increased risk of dying from lung cancer, a meta-analysis showed.46

Welding fumes are classified by IARC as a cause of lung cancer,2 and working as a welder accounted for around 150 lung cancer deaths in Britain in 2005.27 Welders have a 26% increased risk of lung cancer, a meta-analysis showed.47

Working with arsenic and inorganic arsenic compounds causes lung cancer, IARC states.2 These exposures caused around 110 lung cancer deaths in Britain in 2005, it is estimated.27 These substances are again common in metal production, but also have some agricultural applications, including production and use of arsenic-containing pesticides, wood preservation, and are naturally present at low levels in soil. Arsenic and smoking also appear to have a synergistic effect on lung cancer risk: arsenic exposure increases lung cancer risk more in smokers than in non-smokers.35,48,49

IARC classifies a number of other workplace exposures as causes of lung cancer. These include metals (beryllium and compounds; aluminium production; cadmium and compounds; chromium compounds; nickel compounds; plutonium); organic compounds (Bis(chloromethyl)ether; Chloromethyl methyl ether; sulphur mustard); and exposures in underground hematite mining and rubber production.2 Most of these exposures are thought to have affected a small number of workers in Britain, and there are no estimates for the number of lung cancer deaths linked to them in Britain.27

Rock wool and glass wool production workers appear to have a slightly increased risk of lung cancer, a meta-analysis found.50 But residual confounding by smoking and asbestos exposure may explain part of the observed increase, and end-users of rock wool and glass wool have not been shown to have an increased risk.50 IARC states that the effect of these exposures on lung cancer risk is presently not classifiable, because the evidence in humans is insufficient.51

section updated 04/01/13
section updated 04/01/13

Long-term exposure to outdoor very small particles measuring less than 2.5 micrometres in diameter suspended in the air (known as particulate matter or PM2.5) may increase lung cancer mortality risks by 14%, a study in the US has shown.52 Lung cancer death rates are increased by 15% to 21% per 10 microgram per cubic metre (µg/m3) increase in airborne particulate matter, and are also increased in people living near major roads, a meta-analysis showed.53 As described, IARC states that diesel exhaust may increase the risk of lung cancer in the general public, but most evidence for this comes from studies of highly-exposed workers.40

Polluted air inside the home also appears to increase lung cancer risk. Use of coal in the home for cooking or heating around doubles lung cancer risk, meta-analyses have shown.54,55 Most included studies were from China and Taiwan, where the coals used may contain more harmful substances compared with coals used elsewhere; so this risk ratio may not be generalisable to the UK.54 A study including UK participants found no significant effect of domestic coal use.56

section reviewed 04/01/13
section updated 04/01/13

A family history of lung cancer in a first-degree relative was associated with a 51% increased risk of lung cancer, independent of smoking and other relevant factors, a meta-analysis showed.57

The effect is stronger when the affected relative is a sibling (82% risk increase) rather than a parent (25-37% risk increase).57

section reviewed 04/01/13
section updated 04/01/13

Radiotherapy treatment for a previous cancer is associated with around 320 lung cancer cases in the UK each year, it is estimated.28,58 A substantial proportion of these previous cancers were breast cancers, due in large part to the high prevalence of breast cancer.

People who had radiotherapy for breast cancer have an increased lung cancer risk, particularly if they are also smokers.59 However, modern radiotherapy techniques for breast cancer do not show a clear effect, and nor does chemotherapy.59 Recent research shows the association between lung and breast cancers may be restricted to ER-negative breast cancer, perhaps indicating shared causal factors in addition to the radiotherapy effect.60

Treatment for Hodgkin lymphoma increases lung cancer risk by 2.6-7 times.65,66 This effect seems stronger in smokers than non-smokers, and stronger for treatment with chemotherapy plus radiotherapy compared to chemotherapy alone.65,66

Increased risk of lung cancer has also been shown after treatment for non-Hodgkin lymphoma (with some evidence that this varies by non-Hodgkin’s lymphoma subtype);67,68 testicular cancer (up to 30 years after diagnosis);69 and uterine sarcomas.70

section reviewed 04/01/13
section updated 04/01/13

People with HIV or AIDS have almost three times the risk of lung cancer, meta-analyses have shown.71,72 This effect appears to be independent of smoking, as some studies which adjust for smoking behaviour still find an elevated risk for HIV and AIDS patients.72,73 The effect appears to be slightly stronger for people with AIDS than for people with HIV, and slightly stronger for women than for men.72

The risk of lung, trachea and bronchus cancer is around doubled in people who have had an organ transplant, a meta-analysis and large cohort study have reported.71,74

A history of pneumonia is associated with 36% increased lung cancer risk in never-smokers, and a 43% increase in ever- and never-smokers combined, a meta-analysis showed.75 The mechanism of this effect is unclear, but may involve the infectious bacteria Chlamydia pneumoniae, which is associated both with community-acquired pneumonia and lung cancer.76

An increased risk of lung cancer has been shown in people with some autoimmune conditions.77,78 People with systemic lupus erythematosus have in most studies demonstrated up to twice the risk of people without the condition, though some studies report around a tripling of risk.77,78 Rheumatoid arthritis patients have also been shown to be at increased risk.78

People with a previous diagnosis of tuberculosis (TB) have around double the lung cancer risk, and the risk increase is found in those who have never smoked as well as smokers, meta-analyses have shown.75,79 The risk increase persisted for more than 20 years after TB diagnosis, but was restricted to lung adenocarcinoma only, in one of these analyses.79

Taking statins for 4 years or more may slightly increase lung cancer risk, a series of nested case-control studies in the UK has shown.80

Women who take hormone replacement therapy (HRT) and are never-smokers or former smokers may have a slightly decreased risk of lung cancer, a meta-analysis found; however this effect was only seen in case-control studies, with no significant effect in cohort studies.81 In contrast, use of combined (oestrogen + progesterone) HRT for 10 years or more was associated with a 50% increase in lung cancer risk, in a large cohort study published after the review.82

section reviewed 04/01/13
section updated 04/01/13

Diet, supplements and alcohol

It is difficult to dissociate the effects of diet and smoking in relation to lung cancer risk. Dietary habits may vary between lung cancer patients and healthy people, and between smokers and non-smokers, creating complex associations. And the effect of smoking is so large, and the effect of dietary factors so small in comparison, that even with detailed adjustment, it is very difficult to avoid residual confounding by tobacco exposure.83 So it remains unclear whether any of the apparent associations which have been seen, are true.

In 2007, the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) reviewed evidence on associations between foods and supplements and lung cancer risk.84 Evidence for most of the associations was classified as limited, and for a number of foods no conclusions were drawn due to poor evidence quality and availability. WCRF/AICR states there is limited-suggestive evidence that red meat, processed meat, total fat, butter and retinol (vitamin A) supplements (in smokers only), may increase the risk of lung cancer;84 and limited evidence that non-starchy vegetables, selenium in foods (e.g. nuts, cereals and meat) or supplements, and foods containing quercetin may protect against lung cancer.84

WCRF/AICR also states there is probable evidence that fruit (particularly fruit containing carotenoids) protects against lung cancer. It is estimated that around 9% of lung cancers in the UK in 2010 were linked to people eating less than 2-3 portions a day (around 160-240g) of fruit.85

Lung cancer risk has also been explored in relation to folic acid (with and without vitamin B12) supplementation,86,87 circulating vitamin B6 and methionine levels,88 and foods containing soy.89

Alcohol intake is not associated with lung cancer risk in never-smokers or ever-smokers, meta-analyses have shown.90,91

Physical activity

Higher levels of physical activity are associated in most studies with 20-40% reductions in lung cancer risk.92 However, the effect is stronger in smokers than non-smokers, and confounding by smoking is a strong possibility.92 If there is a true association it appears that vigorous physical exertion, rather than general daily activity, may be required to obtain benefit,93 although having moderate or high levels of recreational physical activity were both associated with a lower risk of lung cancer (13% and 30% reduction, respectively) in a meta-analysis.94

Medical conditions and medicines

Multiple sclerosis patients appear to have a reduced risk of lung cancer, according to a meta-analysis.95 This is despite the fact that smoking is implicated in the aetiology of both diseases.95

People with asthma have a higher risk of being diagnosed with lung cancer in the two years following their asthma diagnosis, a pooled analysis shows.96 But there is no significant association for people diagnosed with asthma 10 years or more previously, suggesting that misdiagnosis of early lung cancer symptoms as asthma may largely explain the observed effect.96

Aspirin may reduce the risk of lung cancer, though various meta-analyses and pooled analyses show the effect appears to be limited to case-control studies,97,98 lower-quality studies,98 users of 7+ aspirin tablets per week,99 and men.100 Among male ever-users of any non-steroidal anti-inflammatory drugs (NSAIDs), the protective effect was stronger in ever-smokers.100 Non-aspirin NSAIDs show no effect on lung cancer risk.99,100 Because of the potential adverse consequences of high intake of aspirin, such as gastrointestinal haemorrhage, it would not be recommended as a prophylactic measure.

The number of children a women has given birth to is not associated with her risk of lung cancer, a meta analysis showed.101

Endotoxins

Occupational exposure to endotoxins, for example in the cotton textile industry and agriculture, may protect against lung cancer. Lung cancer risks were 28-38% lower among workers in these occupations according to a meta-analysis.102 And lung cancer risk was halved at the highest level of cumulative exposure in a UK cohort study of cotton workers.103

section reviewed 04/01/13
section updated 04/01/13