It is well established that cigarette smoking causes cancer. Epidemiological surveys have shown that smoking is an important causative factor for lung cancer, especially squamous epithelial cell carcinoma and small cell undifferentiated carcinoma. The risk of lung cancer is 13 times higher for smokers than for nonsmokers, and if the daily
If smokers smoke more than 35 cigarettes per day, the risk is 45 times higher than that of nonsmokers. The lung cancer mortality rate for smokers is 10 to 13 times higher than for nonsmokers. About 85% of lung cancer deaths are caused by smoking. Smokers who are also exposed to chemical carcinogens (such as asbestos, nickel, uranium, and arsenic) have a higher risk of developing lung cancer. The polycyclic aromatic hydrocarbons in tobacco smoke need to be metabolized by polycyclic aromatic hydrocarbon hydroxylase before they are cytotoxic and mutagenic, and the concentration of this hydroxylase is higher in smokers than in nonsmokers. Smoking decreases the activity of natural killer cells, thereby reducing the body’s ability to monitor, kill, and remove tumor cell growth, which further explains why smoking is a high risk factor for the development of many cancers. The incidence of laryngeal cancer is more than ten times higher in smokers than in nonsmokers. There is a 3-fold increase in the incidence of bladder cancer, which may be related to the beta-naphthylamine in smoke. In addition, smoking is associated with the occurrence of lip, tongue, oral cavity, esophagus, stomach, colon, pancreatic, kidney, and cervical cancers. Clinical studies and animal studies have shown that the carcinogens in smoke can also affect the fetus through the placenta, resulting in a significant increase in cancer incidence in the offspring.