There are two majors types of lung cancer – small cell and non-small cell lung cancer. Both affect different types of cells in the lung and grow and spread in different ways.

Small cell cancer, also called oat cell lung cancer, or undifferentiated carcinoma is the most lethal of lung cancers. It is virtually never found in a non-smoker. Non-small cell lung cancer, the most common type of lung cancer, is usually associated with a history of smoking, passive smoking, or exposure to radon.

The cancer can be limited, meaning that it is confined to a portion of the chest, or extensive, meaning that it has spread throughout, or from, the chest.

Tumours found in the lungs sometimes originate in cancer elsewhere in the body. In these cases, treatment will be different from that for cancer that originates in the lungs.

Non-small cell lung cancer is described using four stages. In stage one, it is confined to the lung, in stages two and three it is confined to the chest; and in stage four the cancer has spread from the chest.