Lung Cancer Risk Factors Lung cancer is the most commonly diagnosed cancer in the world, accounting for 12.7% of all new cancers cases annually (McErlean and Ginsberg, 2011, p. 173). Lung cancer is also the most lethal, killing more people each year (18.2%) that any other type of cancer (Molina, Yang, Cassivi, Schild, and Adjei, 2008, p. 584; Brennan, Hainaut, and Boffetta, 2011, p. 399). There are very large geographical differences (30 to 60-fold) in the prevalence of lung cancer, with developing countries representing a full 55% of all new cases each year (McErlean and Ginsberg, 2011, p. 173). The geographical difference in incidence highlights the dominance of environmental risk factors in lung cancer etiology.

Types of Lung Cancer

Non-small cell lung cancer (NSCLC) is the most common type, representing 85% of all lung cancers (Molina, Yang, Cassivi, Schild, and Adjei, 2008, p. 584). The three types of NSCLC are squamous-cell carcinoma, adenocarcinoma, and large-cell carcinoma, with the first two types representing 80% of all lung cancer cases (Brennan, Hainaut, and Boffetta, 2011). The second most common type of lung cancer is small-cell lung carcinoma (SCLC). The main difference between NSCLC and SCLC are the cell types of origin, with the former arising from bronchial epithelial-cell precursors and the...

174-175). This is due to the presence of several carcinogens in tobacco smoke. Since these compounds are also present in second-hand smoke the risk of lung cancer for non-smoking bystanders is significantly elevated compared to unexposed non-smokers. Squamous-cell carcinoma and SCLC have been found to be associated more frequently with tobacco smoke exposure, although this difference is non-significant. The incidence of squamous-cell carcinoma and adenocarcinoma is declining and increasing, respectively, and is believed to be related to how the composition of cigarettes have changed over time.
Exposure to indoor radon gas is the second leading cause of lung cancer (McErlean and Ginsberg, 2011, p. 175). The ground in some geographic areas can produce significant amounts of radon gas that is otherwise diluted in the atmosphere, but if a building is constructed on top of these sources the gas can become trapped inside and expose inhabitants to high concentrations. Mine workers may also be exposed to significant concentrations of radon and other radioactive compounds. Inhalation of radon exposes…