Lung cancer is the second frequent cause of cancer in men and the third most common cancer in women.*  One out of every five persons who died from cancer had lung cancer. An estimated 85% of lung cancer cases in males and 75% in females are caused by cigarette smoking. Less than 10% of lung cancers occur among non-smokers. The risk of lung cancer for the smoker is 15 to 25 times increased. When the smoker stops smoking, the risk of lung cancer dropped to 2 times the risk of a non-smoker after 10 to 15 years. The best safeguard against lung cancer is never to smoke, and if you smoke, stop smoking now. 

The Healthy Lung The air we breathe in enter the lungs through the trachea and then the right and left bronchi. The bronchi are airways that branch into smaller airways and finally the air sacs. Oxygen is absorbed and carbon dioxide expelled via the surface area of the air sacs. The average lung has more than 300 million of these air sacs.

Mucus produced by the cells in the airways trap the foreign materials that enter the airway. Tiny hair-like structures called cilia sweep the mucus toward the throat where it can be coughed out. 

The Smoked-Damage Lung

Consistent insult e.g. due to smoking, to the cell lining of the airway will cause an increase in the production of mucus. The tiny-hair in the air passages become worn away and are unable to sweep foreign particles out of the throat. Very often the smoker tries to cough out the mucus. Chronic smokers have been heard to cough frequently in the morning. In more advanced cases, the air sacs become destroyed and abnormal growth patterns leading to cancer may develop. 

The Cancerous Lung

Lung cancer can take 10 to 30 years to develop. Hence it is frequently seen in middle-aged and elderly persons. In lung cancer, the cells lining the airways grow and divide without control so that an abnormal mass is formed. The cancer cells grow and spread to the other parts of the body. Lung cancers tend to spread more quickly because the lungs are supplied richly by blood vessels and lymphatic vessels. When the cancer spreads through the lymph channels, it can cause enlarged lymph glands. When it spreads through the blood stream, the cancer cells spread to the liver, bone, brain or the other lung. 

* Singapore Cancer Registry, Interim Report, 2001-2005