What Causes Lung Cancer?
Lung cancer is a multistep process that involves cancer-causing agents (environmental carcinogens), inherited genes, and tumor promoters (e.g., inflammatory mediators) (Miller YE 2005; Philip M et al 2004; Tokuhata GK et al 1963). Cigarette smoking may cause as many as 90 percent of male and 79 percent of female lung cancers (Ozlu T et al 2005).
Smoking. Cigarette smoke contains potent cancer-causing derivatives of nicotine, and nicotine itself is directly involved in lung cancer development (Minna JD 2003). Smoking cessation is difficult because nicotine is highly addictive; however, nicotine replacement therapy combined with Zyban® (bupropion) enables a higher smoking cessation rate (L F et al 2005). Medicinal herbal tea made from cloves and milk vetch reduces smoking withdrawal symptoms and increases the rate of smoking cessation (Lee HJ et al 2005). In 2006, the Food and Drug Administration approved a new smoking cessation drug called Chantix™ (varenicline). This new drug is the first prescription medication approved for smoking cessation in almost a decade. It works by partially activating the nicotine receptors in the brain, thus reducing the craving for nicotine and reducing withdrawal symptoms. It also reduces the satisfaction gained by smoking, which may lessen addiction.
Nonsmokers get lung cancer too. Nonsmokers make up 10 to 15 percent of all lung cancer cases (Vastag B 2006). Many nonsmokers who develop lung cancer appear to carry a genetic tendency (Gorlova OY et al 2006).
Some cancer risk is inherited. A two- to threefold increase in lung cancer risk is associated with having a relative with lung cancer (Matakidou A et al 2005). Adults with retinoblastomas (inherited mutations in the retinoblastoma-1 (RB1) gene) and those with Li-Fraumeni syndrome (inherited mutations in the tumor suppressor p53 gene) may develop lung cancer (typically bronchial cancers) at a higher rate than the general population, suggesting a family association (Kleinerman RA et al 2000; Zalcman G et al 1994). The p53 and RB1 genes are both mutated in more than 90 percent of SCLCs, while p53 is mutated in more than 50 percent and RB1 in 20 percent of NSCLCs (Campling BG et al 2003; Horowitz JM et al 1990).
Some lung cancer is caused by exposure to toxins and viruses
. Indoor exposure to secondhand smoke, radon gas, asbestos, and heavy metals (e.g., arsenic, nickel, chromium, iron oxide) and exposure to petrochemicals, polycyclic aromatic hydrocarbons, and human papillomavirus all cause lung cancer (Miller YE 2005; Vukovic B et al 2005; Chen YC et al 2004; Minna JD et al 2002; Hertz-Picciotto I et al 1993).