Lung cancer

Lung cancer is a malignant tumour of the lungs. Most commonly it is bronchogenic carcinoma (about 90%). Lung cancer is the most lethal malignant tumour worldwide, causing up to 3 million deaths annually.

Causes

Exposure to carcinogens, such as those present in tobacco smoke, immediately causes cumulative changes to the tissue lining the bronchi of the lungs (the bronchial mucous membrane) and more tissue gets damaged until a tumour develops.

Related Topics:
Carcinogen - Tobacco smoke - Bronchi

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There are four major causes of lung cancer (and, actually, cancer in general):

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• Carcinogens such as those in cigarette smoke
• Radiation exposure
• Genetic susceptibility
• Viral infection

The role of smoking

Smoking, particularly of cigarettes, is believed to be by far the main cause of lung cancer, which at least in theory makes it one of the easiest diseases to prevent. An estimated 80% of lung cancers result from smoking due to the hundreds of known carcinogens—such as polynuclear aromatic hydrocarbons—present in cigarette smoke. The length of time a person continues to smoke as well as the amount smoked increases the person's chances of contracting lung cancer. If a person stops smoking, these chances steadily decrease as the lung damage is repaired.

Related Topics:
Smoking - Cigarette - Aromatic hydrocarbon

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Passive smoking—the inhalation of smoke from another's smoking—has recently been identified as a much larger cause of lung cancer in non-smokers than previously believed. The US Environmental Protection Agency (EPA) in 1993 concluded that about 3,000 lung cancer-related deaths a year were caused by passive smoking, however since this report was declared null and void by a federal judge in 1998, the true extent is still contested by scientists.

Related Topics:
Passive smoking - US Environmental Protection Agency

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Asbestos

Asbestos can cause a variety of lung diseases. It increases the risk of developing lung cancer. There is a synergistic effect between tobacco smoking and asbestos in the formation of lung cancer.

Related Topics:
Asbestos - Synergistic

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Asbestos can also cause cancer of the pleura, called mesothelioma.

Related Topics:
Pleura - Mesothelioma

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Radioactivity

Radon is a colorless and odorless gas generated by the breakdown of radioactive radium, which in turn is the decayed product of uranium, found in the earth's crust. Radon exposure is the second major cause of lung cancer after smoking. The radiation ionizes genetic material, causing mutations that sometimes turn cancerous. Radon gas levels vary by locality and the composition of the underlying soil and rocks. For example, in areas such as Cornwall in the UK (which has granite as substrata), radon gas is a major problem, and buildings have to be force-ventilated with fans to lower radon gas concentrations. In the US, the EPA estimates that one in 15 homes has radon levels above the recommended standard.

Related Topics:
Radon - Radium - Uranium - Crust - Ion - Cornwall - Granite

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Genetics and viruses

Oncogenes are genes that are believed make people more susceptible to cancer. Proto-oncogenes are believed to turn into oncogenes when exposed to particular carcinogens. Viruses are also suspected of causing cancer in humans, as this link has already been proven in animals. Genetic susceptibility and viral infection are not of major importance in lung cancer, but they may influence pathogenesis.

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