Lung cancer is the uncontrolled growth of abnormal cells in the lung. Majority of people who get lung cancer have been cigarette smokers, but not all people who smoke get lung cancer. And, some people who have never smoked get lung cancer. Normal lung tissue is made up of cells that are programmed by nature to create lungs of a certain shape and function.

Sometimes the instructions to a cell go haywire and that cell and its offspring reproduce wildly, without regard for the shape and function of a lung. That wild reproduction can form tumors that clog up the lung and make it stop functioning as it should. Because of the large size of the lungs, cancer may grow for many years, undetected, without causing suspicion. Lung cancer can spread outside the lungs without causing any symptoms. Adding to the confusion, the most common symptom of lung cancer, a persistent cough, can often be mistaken for a cold or bronchitis.

In men who die of lung cancer (squamous and undifferentiated), all of whom were smokers, the remainder of the epithelial lining shows changes that may be considered as preliminary stages to the development of lung cancer, including early invasion. There are few such changes in nonsmokers, but they increase rapidly with the amount of cigarette smoking.

-Oscar Auerbach, Arthur Purdy Stout, Edward Cuyler Hammond, Lawrence Garfinkel, 1964

Lung cancer is not infectious and cannot be passed on to other people.

Cigarette smoking is known to be the cause of majority of lung cancers. The risk of developing the disease increases with the number of cigarettes smoked, and starting to smoke at a young age. If a person stops smoking, the risk of lung cancer is greatly reduced that is his or her chances of developing the disease are similar to that of a non-smoker after 15 years. 

Lung cancer has always been more common in men, particularly over the age of 40. In recent years more women have started smoking, the number of women developing the disease has increased considerably.

Inhaling other people's cigarette smoke, which is known as passive smoking, slightly increases the risk of lung disease and cancer, although the risk is still much less than if one is a smoker. In some families smokers may be more prone to developing lung cancer due to a genetic link.

Exposure to certain chemicals and substances such as asbestos, uranium, chromium and nickel has been linked to lung cancer, but these are very rare causes. Though air pollution has been suspected as a cause of lung cancer it has been difficult to prove.

Surgery, radiotherapy and chemotherapy may be used separately, or together, to treat cancer of the lung. Surgery is the primary therapy (a lobe or part of the lung is removed). Radiotherapy is used occasionally for a long term control of disease. Treatment should be decided by taking into consideration a number of factors including your general health, the type and size of the tumor, what it looks like under the microscope and whether it has spread beyond the lung.

Biopsy - A test in which a piece of tissue is removed either by surgery or through a needle and examined under a microscope to determine if the cells are cancerous and to identify the type of cancer. 

Bronchoscopy - Endoscopy procedure of the bronchial passage of the lungs. 

Chemotherapy - Treatment with anticancer drugs. 

Radiation Therapy - Treatment using X-rays, radium, neutrons, or other types of cell-destroying radiation. 

Side Effect - A secondary, unintended, and usually unpleasant effect, as from a drug or other treatment; for example, nausea is a side effect of some anticancer drugs. 

Sputum Cytology - Examination under a microscope of cells coughed up from the lungs or breathing tubes. 

Tumor - An abnormal mass of tissue that results from excessive cell division. Tumors perform no useful body function. They may be either benign (not cancer) or malignant (cancer).