Lung cancer
Other namesLung carcinoma
LungCACXR.PNG
A chest X-ray showing a tumor in the lung (marked by arrow)
SpecialtyOncology
SymptomsCoughing (including coughing up blood), weight loss, shortness of breath, chest pains[1]
Usual onset~70 years[2]
TypesSmall-cell lung carcinoma (SCLC), non-small-cell lung carcinoma (NSCLC)[3]
Risk factors
Diagnostic methodMedical imaging, tissue biopsy[6][7]
TreatmentSurgery, chemotherapy, radiotherapy[7]
PrognosisFive-year survival rate 17.4% (US)[2]
Frequency3.3 million affected as of 2015[8]
Deaths1.7 million (2015)[9]

Lung cancer, also known as lung carcinoma,[7] is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung.[10] This growth can spread beyond the lung by the process of metastasis into nearby tissue or other parts of the body.[11] Most cancers that start in the lung, known as primary lung cancers, are carcinomas.[12] The two main types are small-cell lung carcinoma (SCLC) and non-small-cell lung carcinoma (NSCLC).[3] The most common symptoms are coughing (including coughing up blood), weight loss, shortness of breath, and chest pains.[1]

The vast majority (85%) of cases of lung cancer are due to long-term tobacco smoking.[4] About 10–15% of cases occur in people who have never smoked.[13] These cases are often caused by a combination of genetic factors and exposure to radon gas, asbestos, second-hand smoke, or other forms of air pollution.[4][5][14][15] Lung cancer may be seen on chest radiographs and computed tomography (CT) scans.[7] The diagnosis is confirmed by biopsy which is usually performed by bronchoscopy or CT-guidance.[6][16]

Avoidance of risk factors, including smoking and air pollution, is the primary method of prevention.[17] Treatment and long-term outcomes depend on the type of cancer, the stage (degree of spread), and the person's overall health.[7] Most cases are not curable.[3] Common treatments include surgery, chemotherapy, and radiotherapy.[7] NSCLC is sometimes treated with surgery, whereas SCLC usually responds better to chemotherapy and radiotherapy.[18]

Worldwide in 2012, lung cancer occurred in 1.8 million people and resulted in 1.6 million deaths.[12] This makes it the most common cause of cancer-related death in men and second most common in women after breast cancer.[19] The most common age at diagnosis is 70 years.[2] Overall, 17.4% of people in the United States diagnosed with lung cancer survive five years after the diagnosis,[2] while outcomes on average are worse in the developing world.[20]

Signs and symptoms

Signs and symptoms which may suggest lung cancer include:[1]

If the cancer grows in the airways, it may obstruct airflow, causing breathing difficulties. The obstruction can lead to accumulation of secretions behind the blockage, and predispose to pneumonia.[1]

Depending on the type of tumor, paraneoplastic phenomena—symptoms not due to the local presence of cancer—may initially attract attention to the disease.[21] In lung cancer, these phenomena may include hypercalcemia, syndrome of inappropriate antidiuretic hormone (SIADH, abnormally concentrated urine and diluted blood), ectopic ACTH production, or Lambert–Eaton myasthenic syndrome (muscle weakness due to autoantibodies). Tumors in the top of the lung, known as Pancoast tumors, may invade the local part of the sympathetic nervous system, leading to Horner's syndrome (dropping of the eyelid and a small pupil on that side), as well as damage to the brachial plexus.[1]

Many of the symptoms of lung cancer (poor appetite, weight loss, fever, fatigue) are not specific.[6] In many people, the cancer has already spread beyond the original site by the time they have symptoms and seek medical attention.[22] Symptoms that suggest the presence of metastatic disease include weight loss, bone pain and neurological symptoms (headaches, fainting, convulsions, or limb weakness).[1] Common sites of spread include the brain, bone, adrenal glands, opposite lung, liver, pericardium, and kidneys.[22] About 10% of people with lung cancer do not have symptoms at diagnosis; these cancers are incidentally found on routine chest radiography.[16]

Causes

Relationship between cigarette consumption per person (blue) and male lung cancer rates (dark yellow) in the US over the century.
Risk of death from lung cancer is strongly correlated with smoking

Cancer develops after genetic damage to DNA and epigenetic changes. Those changes affect the cell's normal functions, including cell proliferation, programmed cell death (apoptosis), and DNA repair. As more damage accumulates, the risk of cancer increases.[23]

Smoking

Tobacco smoking is by far the main contributor to lung cancer.[4] Cigarette smoke contains at least 73 known carcinogens,[24] including benzo[a]pyrene,[25] NNK, 1,3-butadiene, and a radioactive isotope of polonium – polonium-210.[24] Across the developed world, 90% of lung cancer deaths in men and 70% of those in women during the year 2000 were attributed to smoking.[26] Smoking accounts for about 85% of lung cancer cases.[7]

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 either living or working with a smoker. Studies from the US,[27][28][29] Europe,[30] and the UK[31] have consistently shown a significantly-increased risk among those exposed to passive smoking.[32] 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.[33] Investigations of sidestream smoke suggest that it is more dangerous than direct smoke.[34] Passive smoking results in roughly 3,400 lung cancer-related deaths each year in the U.S.[29]

Marijuana smoke contains many of the same carcinogens as those in tobacco smoke.[35] However, the effect of smoking cannabis on lung cancer risk is not clear.[36][37] A 2013 review did not find an increased risk from light to moderate use.[38] A 2014 review found that smoking cannabis doubled the risk of lung cancer.[39]

Radon gas

Radon is a colorless 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 become cancerous. Radon is the second-most common cause of lung cancer in the US,[40] causing about 21,000 deaths each year.[41] The risk increases 8–16% for every 100 Bq/ increase in the radon concentration.[42] Radon gas levels vary by locality and the composition of the underlying soil and rocks. About one in 15 homes in the US have radon levels above the recommended guideline of 4 picocuries per liter (pCi/l) (148 Bq/m³).[43]

Asbestos

Asbestos can cause a variety of lung diseases such as lung cancer. Tobacco smoking and asbestos both have synergistic effects on the development of lung cancer.[5] In smokers who work with asbestos, the risk of lung cancer is increased 45-fold compared to the general population.[44] Asbestos can also cause cancer of the pleura, called mesothelioma – which actually is different from lung cancer.[45]

Air pollution

Outdoor air pollutants, especially chemicals released from the burning of fossil fuels, increase the risk of lung cancer.[4] Fine particulates (PM2.5) and sulfate aerosols, which may be released in traffic exhaust fumes, are associated with a slightly-increased risk.[4][46] For nitrogen dioxide, an incremental increase of 10 parts per billion increases the risk of lung cancer by 14%.[47] Outdoor air pollution is estimated to cause 1–2% of lung cancers.[4]

Tentative evidence supports an increased risk of lung cancer from indoor air pollution in relation to the burning of wood, charcoal, dung, or crop residue for cooking and heating.[48] Women who are exposed to indoor coal smoke have roughly twice the risk, and many of the by-products of burning biomass are known or suspected carcinogens.[49] This risk affects about 2.4 billion people worldwide,[48] and it is believed to result in 1.5% of lung cancer deaths.[49]

Genetics

About 8% of lung cancer is caused by inherited factors.[50] In relatives of people that are diagnosed with lung cancer, the risk is doubled, likely due to a combination of genes.[51] Polymorphisms on chromosomes 5, 6, and 15 are known to affect the risk of lung cancer.[52] Single-nucleotide polymorphisms (SNPs) of the genes encoding the nicotinic acetylcholine receptor (nAChR) – CHRNA5, CHRNA3, and CHRNB4 – are of those associated with an increased risk of lung cancer, as well as RGS17 – a gene regulating G-protein signaling.[52]

Other causes

Numerous other substances, occupations, and environmental exposures have been linked to lung cancer. The International Agency for Research on Cancer (IARC) states that there is some "sufficient evidence" to show that the following are carcinogenic in the lungs:[53]

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https://en.wikipedia.org/wiki/Lung_cancer