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Lung carcinoma is one of the major problems of modern society. In the United States, it causes about 140,000 deaths annually; in England and Wales, it accounts for 40,000 deaths annually—about one-third of total cancer deaths and almost one-tenth of all deaths from any cause. The incidence has increased markedly since 1950 (approximately fivefold) and continues to increase. Rates of lung cancer vary greatly in different countries, principally due to differences in smoking habits.
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Lung carcinoma is more common in males; the male:female ratio was 7:1 in 1960 but has fallen to about 2:1. Lung cancer has overtaken breast cancer as the leading cause of death by cancer in women. It is a disease of older individuals, being rare under 40 years of age.
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Cigarette smoking is the main cause of lung carcinoma (Chapter 12: Disorders Due to Chemical Agents). Heavy cigarette smokers (over 40 cigarettes a day) have a 20-fold increase in incidence compared to nonsmokers. Cessation of smoking decreases the risk: 10 years after stopping smoking, the risk falls to that of a nonsmoker. The risk is only slightly less with “low-tar” filter cigarettes. Cigar smoking and pipe smoking carry a much lower risk (probably because of less smoke inhalation).
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The mechanism by which smoking causes lung carcinoma is not clear. A large number of potent carcinogens are present in cigarette smoke, including polycyclic hydrocarbons, aromatic amines, and heavy metals such as nickel. Any or all of these may be involved in human carcinogenesis (Chapter 18: Neoplasia: II. Mechanisms & Causes of Neoplasia).
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Cigarette smoking produces changes in the respiratory epithelium of humans. There is loss of cilia and progression from squamous metaplasia through all degrees of dysplasia to carcinoma in situ. Squamous metaplasia alone is not premalignant, but dysplasia is. Dysplasia is very uncommon in nonsmokers. In patients with lung carcinoma, the respiratory epithelium away from the neoplasm frequently shows dysplasia and carcinoma in situ.
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Cigarette smoking is most strongly associated with squamous carcinoma and small cell undifferentiated carcinoma and to a lesser degree with adenocarcinoma.
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Industrial Carcinogens
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The best-known occupational lung carcinogen is asbestos, exposure to which increases the risk of lung carcinoma as documented among World War II shipyard workers (Chapter 35: The Lung: II. Toxic, Immunologic, & Vascular Diseases). The risk of lung cancer following asbestos exposure is compounded by cigarette smoking.
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Mining of many different heavy metals (eg, uranium, nickel, chromate, gold) is also associated with an increased risk of lung cancer.
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Historically, the miners of Jstocáchymov in the Czech Republic and Schneeberg in Germany were described as developing “mountain sickness” for 4 centuries before it was realized that the sickness was lung carcinoma from ...