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Smoking and Malignant GI Cancers

Dr. Wu Qi, Chief Physician, Endoscopy Center of Peking University Cancer Hospital, Beijing, China

There are more than 1400 ingredients within cigarettes. Smoking cigarettes causes smoke which contains more than 40 different substances that cause cancers, and more than 10 different substances that promote cancerous cell growing. Among these substances, the most harmful to human health are nicotine, tar, carbon monoxide, and several types of metallic chemicals. The nicotine amount within one cigarette can kill a healthy rat. The large amount of carbon monoxide from smoke has a 240-300 times stronger binding capability with hemoglobin than the oxide does. This will seriously destroy the oxygen-carrying capacity of the hemoglobin. So, smoking can accelerate the blood coagulation, and may lead to myocardial infarction, stroke, myocardial anoxia, and other cardiovascular diseases. What’s more, smoking can also lead to a higher incidence of upper GI malignant cancers like esophageal cancer and gastric cancer.

Esophageal cancer has high death rates and complex etiology. Its high incidence and aggregation draw many researchers attention on its etiology, however, the etiology hasn’t been made clear so far. Most international researchers take smoking cigarettes as a major risk factor for esophageal cancer. While in China, researchers have different views on cigarettes’ contribution to esophageal cancer. The mechanism of smoking in the development of cancer relates to many cancerous substances within the smoke and tar, such as polycyclic aromatic hydrocarbons, benzpyrene, nitroso compounds, epoxides, polonium, and nicotine etc. These substances directly affect the cell protein and nuclear acid and cause cellular damage and cancer. A meta-analysis of 25 journal articles published from 1993 to 2008 in China was done; their general Relative Risk (RR) and Odds Ratio (OR) were calculated, and this showed that smoking is a risk factor to esophageal cancer incidence. In both males and females, smoking is statistically related to esophageal cancer incidence. Daily dose of smoking and history of smoking both have a dose-response relation to the esophageal cancer. Analysis found that daily dose of smoking and smoking history (20 years or longer) have positive correlations to esophageal cancer incidence. When analyzing the research published, we found that as the years went forward, smoking and esophageal cancer incidence have stronger relevance.

Both international and domestic researchers also found out that smoking cigarettes has strong relation to gastric cancer, and their Relative Risks are form 1.3 to 2.5, and showed a moderate dose-response relation. Although the mechanism of smoking causing gastric cancer hasn’t been made clear, cigarettes and smoke contain several carcinogens like polycyclic aromatic hydrocarbons and nitrosamines. And these two types of substances have been proved in animal labs and confirmed their carcinogenicity. Smoking cigarettes can also delay gastric emptying and cause foods to stay longer in the stomach. Recent research found that tobacco smoke contains free radicals, which can destroy genes, cell membranes, and cause immune function to wane and tissues turn cancer. These free radicals dissolve in saliva and go with digestion down to the stomach, as smoking doses and smoking history increase, cancer will occur. Research results showed that as the smoking years and doses increase, the gastric cancer incidence risks increase too. Even after adjusting the confounding factors, they also have moderate relations to gastric cancer.

It is terrible that in China we have 350 million smokers. In 2002, 66% of male Chinese smoke cigarettes, and 3.08% of female Chinese smoke cigarettes. And the Chinese cigarette smokers group is covering the younger population. More than 50 million adolescents smoke in China. Compared to 1984, the initial age of smoking went down 4-5 years in 2002. In males the initial smoking age went from 22 down to 18, and in females, it went from 25 down to 20. Although the smokers’ percentage from the whole population has dropped a little, the actual smoker population still increased 30 million.

May 31st is the World No-Tobacco Day, we appeal to ban the tobacco advertisements, ban or limit the tobacco companies sponsored events, crack down on tobacco smuggling, prohibit selling cigarettes to adolescents, mandatorily require warning of SMOKE HARMS HEALTH be printed on cigarette boxes, and measures be taken to reduce the passive smoking, so as to let people away from tobacco, away from cancer, away from diseases.