The leading risk factor for lung cancer is smoking. More than 80% of lung cancers are due to cigarette smoking. The longer a person has been smoking and also the more cigarettes a person smokes a day, the greater the risk is for developing lung cancer. Not only are smokers vulnerable to lung cancer, but the people around them are at a greater risk as well due to breathing second-hand smoke. Non-smokers who are married to smokers are at a 30% greater risk than non-smokers who are married to non-smokers. Marijuana cigarettes may also increase the risk of lung cancer since they contain many of the same cancer-causing agents that tobacco cigarettes have and are inhaled more deeply.

Lung cancer most commonly begins in the cells that line your lungs. Smoking causes the majority of lung cancers — both in smokers and in people exposed to secondhand smoke. But lung cancer also occurs in people who never smoked. In these cases, there may be no clear cause of lung cancer. Doctors have identified factors that may increase the risk.

Lung cancer is one of the most common cancers in the world. It is a leading cause of cancer death in men and women in the United States. Cigarette smoking causes most lung cancers. The more cigarettes you smoke per day and the earlier you started smoking, the greater your risk of lung cancer. High levels of pollution, radiation and asbestos exposure may also increase risk.

Causes of Lung Cancer
Smoking: smoking remains the greatest risk factor for lung cancer. Your risk of lung cancer increases with the number of cigarettes you smoke each day and the number of years you have smoked. Quitting at any age can significantly lower your risk of developing lung cancer.

Diet: Scientists are studying many different foods to see how they may change the risk of getting lung cancer. However, any effect diet may have on lung cancer risk is small compared with the risk from smoking. Eating a lot of fat and cholesterol might increase risk of lung cancer. Drinking a lot of alcohol may raise risk as well.

Family History: Studies have found a chromosome that may be responsible for lung cancer. The chromosome can be inherited. If you have had lung cancer before, there is a chance you may develop another type of lung cancer.

Air pollution from vehicles, industry, and power plants can raise the likelihood of developing lung cancer in exposed individuals. Up to 1% of lung cancer deaths are attributable to breathing polluted air, and experts believe that prolonged exposure to highly polluted air can carry a risk similar to that of passive smoking for the development of lung cancer.

Symptoms of Lung Cancer
People often decide to visit the doctor only after they have been bothered by certain complaints over a period of time. Individuals who have lung cancer frequently experience symptoms such as the following:

Metastasis to the bones is most common with small cell type cancers but also occurs with other lung cancer types. Lung cancer that has metastasized to the bone causes bone pain, usually in the backbone (vertebrae), the thighbones, and the ribs.

Shortness of breath usually results from a blockage to the flow of air in part of the lung, collection of fluid around the lung (pleural effusion), or the spread of tumor throughout the lungs.

Chest pain is a symptom in about one-fourth of people with lung cancer. The pain is dull, aching, and persistent and may involve other structures surrounding the lung.

Wheezing or hoarseness may signal blockage or inflammation in the lungs that may go along with cancer.