Cigarette smoking causes most lung cancers, but long term exposure to asbestos is also a cause of lung cancer. People who smoke and have been exposed to asbestos have a very high risk of developing the disease.

There are two main types of lung cancer. Small cell lung carcinoma is common to smokers. Non-small cell lung carcinoma has three main forms, including:

• Squamous cell carcinoma the most common form of lung cancer. This starts in the large air passages, called bronchi.
  
  
• Large cell carcinoma similar to squamous cell carcinoma.
  
  
• Adenocarcinoma starts in glands found in the lining of the airways.