Lung Cancer Risk Factors

What is lung cancer?

Lung cancer is a condition where the lung cells grow uncontrollably and clump together to form a tumour that destroys the healthy cells surrounding it. Globally, it is a significant public health concern and the leading cause of cancer-related deaths with the highest mortality rates among adults. In 2020, approximately 1.8 million deaths were associated with lung cancer.1

Lung cancer is of two types: small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). 

SCLC is always associated with smoking and is usually treated with chemotherapy. NSCLC is the more common type of lung cancer and is responsible for 80% of the cases. NSCLC does not spread to other parts of the body as quickly as SCLC. Carcinoid is a rare form of lung cancer that grows slowly and is usually treated with surgery.

Importance of understanding the risk factors and benefits of cancer screening

Smoking represents the number one risk factor for lung cancer. It is recommended by the American Cancer Society that people between 50 and 80 years get a low-dose computed tomography (LDCT) done every year for lung cancer screening if: 

  • they are smokers 
  • quit smoking in the last 15 years 
  • have been smoking one pack of cigarettes daily for 20 years

The benefit of cancer screening is early-stage detection and catching it before it spreads to other parts of the body, thereby increasing chances of getting cured.2 

Other risk factors do not warrant a screening; however, understanding the risk factors can help you take the necessary precautions to reduce your risk of developing lung cancer. This article briefly touches upon the symptoms and diagnosis and discusses the risks associated with lung cancer in detail.

Symptoms

Lung cancer usually does not present any symptoms until it is in the advanced stages and has spread to other parts of the body. The symptoms vary among individuals and include the following:3

  • A persistent cough that becomes worse
  • Hoarse voice
  • Chest pain
  • Shortness of breath
  • Recurrent lung infections
  • Coughing up blood
  • Weight loss
  • Headaches
  • Loss of appetite
  • Fractures
  • Blood clots

Diagnosis and staging

The diagnosis of lung cancer varies among individuals based on: 

Once the doctor examines your diagnostic test results, the cancer will be assigned a stage that helps to determine the location and size of the tumour and whether the cancer has spread. Accurate staging is crucial as it also helps evaluate the available treatment options and prognosis estimation.5

Lung cancer biomarker testing helps in determining abnormalities in the DNA of the tumour tissue and the levels of certain proteins, which can help doctors provide targeted therapy to the patients.6

Risk factors

Tobacco smoke

The primary cause of lung cancer is smoking tobacco, which is responsible for 90% of lung cancer cases. The risk of lung cancer increases 20-50-fold in smokers compared with those who have never smoked. Although cigarettes are the primary tobacco product, lung cancer has also been seen in people who use cigars, pipes or cigarillos. Additionally, using local tobacco products, such as bidi and hookah (India), water pipes (China) and khii yoo (Thailand) show an increased risk of lung cancer.

African Americans show an increased rate of lung cancer compared with those of different ethnicities in the US. Moreover, China and Japan demonstrate a lower risk of lung cancer compared with those from Europe and North America owing to the recent increase in regular heavy smoking in these countries.

Smokers are not the only people affected by tobacco smoke; non-smokers exposed to second-hand smoke either via a smoker spouse or at the workplace exhibit a 20%-30% increase in lung cancer risk. Even when you smoke occasionally, the risk of lung cancer increases, and it further increases with the frequency and duration of smoking. Thus, completely stopping smoking is the best thing you can do for your health.7,8,9

Radon exposure

Radon exposure is the second main cause of lung cancer as estimated by the US Environmental Protection Agency. Miners are exposed to radon, and thus, are at an increased risk of lung cancer. However, radon exposure is currently more apparent in residential areas compared to a person’s occupation. 

The colourless and odourless gas is naturally present in the soil and enters buildings by passing through cracks or gaps and accumulates in homes. The combination of cigarette smoking and radon exposure has been shown to increase the risk of lung cancer.7,9

Occupational exposure

Lung cancer risk increases in people working in industries where they are exposed to hazardous lung carcinogens, such as: 

  • asbestos
  • heavy metals 
  • silica 
  • diesel exhaust 
  • polycyclic aromatic hydrocarbons

Asbestos

All forms of asbestos are carcinogenic to the lung; however, chrysotile is less potent due to its early clearance. Asbestos was primarily used in the construction industry; however, it was banned in 1999 in the UK, but the possibility of exposure while repairing old buildings containing asbestos persists. Smoking increases lung cancer risk following asbestos exposure.7,8

Silica

Silica is primarily used in the glass- and brick-making industries. Continued exposure causes a condition called silicosis, which increases the risk of lung cancer.7,8

Heavy metals

The following occupations for exposure to the heavy metals present are shown to have a high risk of lung cancer:7

People exposed to chromium [VI] compounds via: 

  • chromate production 
  • chromate pigment manufacturing 
  • chromium plating 
  • ferrochromium production

Those exposed to nickel via: 

  • mining
  • smelting
  • nickel alloy manufacturing 

Those exposed to cadmium via: 

  • battery-making 
  • smelting

Those exposed to arsenic via: 

  • hot smelting 
  • arsenic-containing drinking water 

Diesel exhaust

People, such as mechanics or drivers, who are consistently exposed to diesel engine exhaust fumes have an increased risk of lung cancer.7,8

Polycyclic aromatic hydrocarbons

Burning organic material produces polycyclic aromatic hydrocarbons, which have been associated with an increased risk of lung cancer in people working in industries related to:7 

  • aluminium production 
  • coke production 
  • roofing 
  • chimney sweeping 
  • tar distillation

Air pollution

Indoor air pollution is considered a major risk for lung cancer in nonsmoking people assigned female at birth in Asia who use wood, coal, solid fuels or unrefined cooking oils for cooking in poorly ventilated homes.

Particle pollution comprises small liquid and solid particles in the air generated from power plants, vehicles and forest fires. When you inhale these small particles, they get trapped in the lungs and cause damage, thereby impairing its function.10

Infections or medical conditions

If you have had lung disease before, the risk of lung cancer increases compared with people who have not had it, with the risk increasing in smokers. Patients with chronic obstructive pulmonary disease, tuberculosis and those possessing the Chlamydia pneumoniae infection markers are at high risk of developing lung cancer.7,8

Genetic predisposition

The risk of early-onset lung cancer increases if you have a family history of lung cancer. For example, if immediate family members, such as parents or siblings, who have or have had lung cancer and who are non-smokers, increase the lung cancer risk. It has been shown that individuals who inherit chromosome 6 are at an increased risk of developing lung cancer.

KRAS gene mutations comprise 25% of the gene mutations and is mainly found in smokers and adenocarcinoma patients. EGFR gene mutations are responsible for 30% of gene mutations in lung cancer, primarily found in non-smokers, women and adenocarcinoma patients. The risk of lung cancer is also increased in individuals with Li Fraumeni syndrome, which is characterised by germline mutation in p53, a tumour suppressor gene.11

Diet 

A high intake of total or saturated fats is associated with increased lung cancer risk. Consumption of fried meat or red meat is associated with increased risk, possibly due to the formation of nitrosamines while cooking. 

Research has shown that consuming high doses of beta-carotene or total carotenoids could increase cancer risk, and the risk increases in smokers or past smokers. Drinking more than six cups of coffee is associated with lung cancer in smokers as well.7.8

Sex and age

Lung cancer is usually associated more with people assigned male at birth than people assigned female at birth; however, current research suggests that the incidence of lung cancer is increasing among young and middle-aged people assigned female at birth in the age range of 35–54 years compared with people assigned male at birth in the same age group. Although the prevalence of cigarette smoking, a major cause of lung cancer, does not significantly differ between people in this age group.

Other risk factors, such as air pollution, radon exposure or second-hand smoke, could be responsible for the differences observed between people assigned male at birth and people assigned female at birth. However, the incidence of lung cancer continues to remain high in people assigned male at birth and ≥55 years.12

Summary

Globally, lung cancer is a major cause of mortality in people. Smoking is the main factor responsible for lung cancer and other factors, such as indoor and outdoor air pollution, occupational exposure and diet either independently or in concert with smoking increase lung cancer risk. 

Knowledge of the risk factors can increase awareness and allow people to take adequate precautions, such as lung cancer screening, to reduce the risk of developing lung cancer and detect it at an early stage for effective treatment.

References

  1. World Health Organisation, WHO. Lung cancer. [Internet]. who.int. World Health Organisation. WHO [updated 26 June 2023; cited 31 May 2024]. Available from: https://www.who.int/news-room/fact-sheets/detail/lung-cancer
  2. American Cancer Society. Can lung cancer be found early? [Internet]. cancer.org. American Cancer Society [updated 29 January 2024; cited 31 May 2024]. Available from: https://www.cancer.org/cancer/types/lung-cancer/detection-diagnosis-staging/detection.html 
  3. American Lung Association. Lung cancer symptoms. lung.org. American Lung Association. [Internet]. [updated 7 June 2024; cited 31 May 2024]. Available from: https://www.lung.org/lung-health-diseases/lung-disease-lookup/lung-cancer/symptoms-diagnosis/symptoms
  4. American Lung Association. Lung cancer diagnosis. [Internet]. lung.org. American Lung Association. [updated 7 June 2024; cited 31 May 2024]. Available from: https://www.lung.org/lung-health-diseases/lung-disease-lookup/lung-cancer/symptoms-diagnosis/how-is-lung-cancer-diagnosed
  5. American Lung Association. Lung cancer staging. [Internet]. lung.org. American Lung Association. [updated 7 June 2024; cited 31 May 2024]. Available from: https://www.lung.org/lung-health-diseases/lung-disease-lookup/lung-cancer/symptoms-diagnosis/lung-cancer-staging
  6. American Lung Association. Lung cancer biomarker-testing. [Internet]. lung.org. American Lung Association. [updated 7 June 2024; cited 31 May 2024]. Available from: https://www.lung.org/lung-health-diseases/lung-disease-lookup/lung-cancer/symptoms-diagnosis/biomarker-testing
  7. Malhotra J, Malvezzi M, Negri E, Vecchia CL, Boffetta P. Risk factors for lung cancer worldwide. European Respiratory Journal. 2016. [cited 31 May 2024]; 48(3):889–902. Available from: https://erj.ersjournals.com/content/48/3/889
  8. Cancer Research UK. Risks and causes of lung cancer. [Internet]. cancerresearchuk.org. Cancer Research UK. [updated 14 March 2023; cited 1 June 2024]. Available from: https://www.cancerresearchuk.org/about-cancer/lung-cancer/risks-causes
  9. American Lung Association. Lung cancer causes and risk factors. [Internet]. lung.org. American Lung Association. [updated 7 June 2024; cited 2024 May 31]. Available from: https://www.lung.org/lung-health-diseases/lung-disease-lookup/lung-cancer/basics/what-causes-lung-cancer
  10. American Lung Association. The connection between lung cancer and outdoor air pollution, [Internet]. lung.org. American Lung Association. [updated 30 August 2023; cited 31 May 2024]. Available from: https://www.lung.org/blog/lung-cancer-and-pollution 
  11. Rocky Mountain Cancer Centers. Lung cancer gene mutations: what are they and how do they affect treatment? [Internet]. rockymountaincancercenters.com. Rocky Mountain Cancer Centers. [cited 31 May 2024]. Available from: https://www.rockymountaincancercenters.com/blog/lung-cancer-gene-mutations-what-are-they-and-how-do-they-affect-treatment
  12. Landwher J. What younger and middle-aged women need to know about lung cancer. [Internet]. helath.com. Health. [updated 19 October 2023; cited 31 May 2024]. Available from: https://www.health.com/young-women-lung-cancer-8363009 

Supriya Subramanian

PhD, Life Sciences, MPRS-LM International Max Planck Research School for Living Matter

Supriya has a PhD in Life Sciences from the Max-Planck Institute of Molecular Physiology, Dortmund, Germany. She is a freelance writer and editor with an immense interest in effective science communication. Her goal is to ensure her audience gains a comprehensive understanding of key science areas through her writing. Her experience as an editor reinforces her commitment to providing information that is accurate, clear and concise. Supriya is keen to leverage her writing skills and knowledge to increase health awareness.

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