Causes of lung cancer

Causes[edit]

Graph showing how a general increase in sales of tobacco products in the USA in the first four decades of the 20th century (cigarettes per person per year) led to a corresponding rapid increase in the rate of lung cancer during the 1930s, '40s and '50s (lung cancer deaths per 100,000 male population per year)

Cancer develops following genetic damage to DNA and epigenetic changes. These changes affect the normal functions of the cell, including cell proliferation, programmed cell death (apoptosis) and DNA repair. As more damage accumulates, the risk of cancer increases.^[15]

Smoking[edit]

Cross section of a human lung: The white area in the upper lobe is cancer; the black areas are discoloration due tosmoking.

Smoking, particularly of cigarettes, is by far the main contributor to lung cancer.^[16] Cigarette smoke contains at least 73 knowncarcinogens,^[17] including benzo[a]pyrene,^[18] NNK, 1,3-butadiene and a radioactive isotope of polonium, polonium-210.^[17] Across the developed world, 90% of lung cancer deaths in men during the year 2000 were attributed to smoking (70% for women).^[19] Smoking accounts for 80–90% of lung cancer cases.^[1]

Passive smoking—the inhalation of smoke from another's smoking—is a cause of lung cancer in nonsmokers. A passive smoker can be defined as someone living or working with a smoker. Studies from the US,^[20][21][22] Europe^[23] and the UK^[24] have consistently shown a significantly increased risk among those exposed to passive smoke.^[25] Those who live with someone who smokes have a 20–30% increase in risk while those who work in an environment with secondhand smoke have a 16–19% increase in risk.^[26] Investigations ofsidestream smoke suggest it is more dangerous than direct smoke.^[27] Passive smoking causes about 3,400 deaths from lung cancer each year in the USA.^[22]

Marijuana smoke contains many of the same carcinogens as those in tobacco smoke.^[28] However the effect of smoking cannabis on lung cancer risk is not clear.^[29][30] A 2013 review did not find an increased risk from light to moderate use.^[31] A 2014 review found that smoking cannabis doubled the risk of lung cancer.^[32]

Radon gas[edit]

Radon is a colourless and odorless gas generated by the breakdown of radioactive radium, which in turn is the decay product of uranium, found in the Earth's crust. The radiation decay products ionize genetic material, causing mutations that sometimes turn cancerous. Radon is the second-most common cause of lung cancer in the USA,^[33] causing about 21,000 deaths each year.^[34] The risk increases 8–16% for every 100 Bq/m³ increase in the radon concentration.^[35] Radon gas levels vary by locality and the composition of the underlying soil and rocks. About one in 15 homes in the US has radon levels above the recommended guideline of 4 picocuries per liter (pCi/l) (148 Bq/m³).^[36]

Asbestos[edit]

Asbestos can cause a variety of lung diseases, including lung cancer. Tobacco smoking and asbestos have a synergistic effect on the formation of lung cancer.^[5] In smokers who work with asbestos, the risk of lung cancer is increased 45-fold compared to the general population.^[37] Asbestos can also cause cancer of the pleura, called mesothelioma (which is different from lung cancer).^[38]

Air pollution[edit]

Outdoor air pollution has a small effect on increasing the risk of lung cancer.^[4] Fine particulates (PM_2.5) and sulfate aerosols, which may be released in traffic exhaust fumes, are associated with slightly increased risk.^[4][39] For nitrogen dioxide, an incremental increase of 10parts per billion increases the risk of lung cancer by 14%.^[40] Outdoor air pollution is estimated to account for 1–2% of lung cancers.^[4]

Tentative evidence supports an increased risk of lung cancer from indoor air pollution related to the burning of wood, charcoal, dung or crop residue for cooking and heating.^[41] Women who are exposed to indoor coal smoke have about twice the risk and a number of the by-products of burning biomass are known or suspected carcinogens.^[42] This risk affects about 2.4 billion people globally,^[41] and is believed to account for 1.5% of lung cancer deaths.^[42]

Genetics[edit]

About 8% of lung cancer is due to inherited factors.^[43] In relatives of people with lung cancer, the risk is increased 2.4 times. This is likely due to a combination of genes.^[44]Polymorphisms on chromosomes 5, 6 and 15 are known to affect the risk of lung cancer.^[45]

Other causes[edit]

Numerous other substances, occupations, and environmental exposures have been linked to lung cancer. The International Agency for Research on Cancer (IARC) states there is "sufficient evidence" to show the following are carcinogenic in the lungs:^[46]

• Some metals (aluminum production, cadmium and cadmium compounds, chromium(VI) compounds, beryllium and beryllium compounds, iron and steel founding, nickel compounds, arsenic and inorganic arsenic compounds, underground hematite mining)
• Some products of combustion (incomplete combustion, coal (indoor emissions from household coal burning), coal gasification, coal-tar pitch, coke production, soot, diesel engine exhaust)
• Ionizing radiation (X-radiation, gamma radiation, plutonium)
• Some toxic gases (methyl ether (technical grade), Bis-(chloromethyl) ether, sulfur mustard, MOPP (vincristine-prednisone-nitrogen mustard-procarbazine mixture), fumes from painting)
• Rubber production and crystalline silica dust