TOBACCO AND CANCERS

In many countries cancer is the second most important cause of death. In the U.S.A. and many developed countries, it accounts for 20 percent of all deaths. It is estimated that a million of the 6 million new cases of cancer that occur worldwide annually are caused by the chewing and smoking of tobacco. It is also estimated that 30-40 percent of all cancers are related to tobacco which makes it the most important single factor in cancer causation. The death toll due to malignant disease in the U.S.A. amounts to 400,000-450,000 annually of which 100,000 are due to lung cancer, 85 to 90 percent of this is due to cigarette smoking.

No other single agent which has been examined in as much detail, is more firmly established as a causal agent or as responsible for more cancer deaths than cigarette smoking.The risk of cigarette smokers developing lung cancer increases with the number of cigarettes smoked, the duration of smoking, and the type of smoking done. Approximately one sixth of those who smoke two packs of cigarettes per day will eventually develop lung cancer. Those who smoke 40 cigarettes per day have a 25 fold increased risk compared to non smokers. Cigarette smoking causes all of the major types of lung cancer including squamous cell carcinoma, adeno carcinoma, oat cell and large cell carcinoma.Cancer of the lung was a rare form of cancer at the beginning of this century, even in developed countries. As smoking increased dramatically among men after World War I and among women after World War II, the incidence of cancer of the lung continued to increase until the seventies, after which in men it began to decrease, but it took another decade for that trend to occur in women. Nevertheless, cancer of the lung is still the primary killing cancer among men and women in manydeveloped and developing countrics In Hong Kong, the rate for women is now the highest in the world. Lung cancer rate in Chinese men, for example, in Shanghai 50.2 per 100,000 which is higher than in many North American and European populations. It is the leading cause of cancer mortality among males in Bulgaria, Cuba, former Czechoslovakia, Egypt, Greece, Hong Kong, Hungary, Israel, Philippines, Poland, Romania, Singapore, Thailand, Uruguay, and Zimbabwe. The risk is particularly high among cigarette smokers, and a clear-cut dose-response relationship has been confirmed. The risk is greater among those who started smoking at a young age and those who smoke high yield tar cigarettes.

Laryngeal cancer is the second cancer caused by cigarette smoking, but the total number of cases is smaller than lung cancer and the survival is much better. Cigarette smokers are five times more likely to develop cancer of the oral cavity and the esophagus compared to non smokers. There is synergism between alcohol and cigarette smoking in causing cancer of the larynx, esophagus and oral cavity.

Cigarette smoking is also an important contributing factor in cancers of the bladder, kidney and pancreas. An association between gastric cancer and smoking has been noted.

Cigarette smoking has even been implicated in cancers of the breast, kidney, liver, cervix, uteri and many others. It is also known to be related to childhood cancer as a result of prenatal exposure to parents’ smoking. Passive smoking has been implicated in many cases of cancer.