About lung cancer

Lung cancer begins when abnormal cells grow and multiply in an uncontrolled way in the lungs. Cancer that starts in the lungs is called primary lung cancer. It can spread throughout the lungs, and to the lymph nodes, pleura, brain, adrenal glands, liver and bones.

When cancer starts in another part of the body and spreads to the lungs, it is named after the primary cancer (e.g. cancer that starts in the breast and spreads to the lungs is called metastatic breast cancer).

This content is about primary lung cancer.

The lungs

The lungs are 2 sponge-like organs that are used for breathing. They are part of the respiratory system, which also includes the nose, mouth, trachea (windpipe) and airways (tubes) to each lung. There are large airways known as bronchi (singular: bronchus) and small airways called bronchioles. The lungs sit in the chest and are protected by the rib cage.

Lobes

Each lung is made up of sections called lobes – the left lung has 2 lobes, and the right lung has 3 lobes.

Diaphragm 

The lungs rest on the diaphragm, which is a wide, thin muscle that helps with breathing, and separates the chest from the abdomen (belly).

Mediastinum 

The space between the two lungs is called the mediastinum. A number of important structures lie in this space, including:

• the heart and large blood vessels
• the trachea – the tube that carries air into the lungs
• the oesophagus – the tube that carries food to the stomach
• lymph nodes – small, bean-shaped structures that collect and destroy bacteria and viruses.

Pleura 

The lungs are covered by 2 thin layers of tissue called the pleura. The inner layer (visceral pleura) lines the lung surface, and the outer layer (parietal pleura) lines the chest wall, mediastinum and diaphragm. The layers are separated by a small amount of fluid that lets them smoothly slide over each other when you breathe. The pleural cavity is the potential space between the 2 layers; there is no space between the layers when the lungs are healthy.

The respiratory system

The different types of lung cancer

There are 2 main types of primary lung cancer: non-small cell lung cancer and small cell lung cancer.

Types of lung cancer

Pleural mesothelioma is a type of cancer that affects the covering of the lung (the pleura). It is different from lung cancer and is usually caused by exposure to asbestos. Other types of cancer, like cancers that start in the chest wall, may also affect the lungs but are not considered lung cancer.

For more on this, see Pleural mesothelioma.

What causes lung cancer?

A risk factor is anything that is known to increase a person’s chances of developing a certain condition, such as cancer. It’s possible to avoid or reduce the impact of some risk factors. Called modifiable risk factors, these include smoking tobacco or exposure to air pollution. Other risk factors, such as having a family history of lung cancer, can’t be avoided.

Not all causes of lung cancer are fully understood, and some people develop lung cancer without having any known risk factors. The factors listed below are known to increase the risk of lung cancer. Having these risk factors does not mean you will develop lung cancer, but if you are concerned, talk to your doctor.

Lifestyle factors

Tobacco smoking – In Australia, about 85% of lung cancer cases in men and 70% in women are estimated to be a result of smoking tobacco. The earlier a person starts smoking, the longer they smoke and the more cigarettes they smoke, the higher the risk of developing lung cancer.

People who have never smoked can also get lung cancer. About 15% of cases occur in men who have never smoked, and about 30% of cases occur in women who have never smoked.

Environmental or work-related factors

Second-hand smoking – Breathing in other people’s tobacco smoke (second-hand smoke) can cause lung cancer. Living with someone who smokes is estimated to increase the risk of lung cancer by up to 30% in people who don’t smoke.

Exposure to asbestos – People who are exposed to asbestos are more likely to develop lung cancer or pleural mesothelioma. Although the use of asbestos in building materials has been banned across Australia since 2004, asbestos may still be found in some older buildings and fences.

Exposure to other elements – People who have been exposed to radioactive gas (radon), such as uranium miners, have an increased risk of lung cancer. Outdoor and indoor air pollution (e.g. exposure to household air pollution from gas or wood-burning cooking or heating) is another risk factor. Contact with the processing of arsenic, silica, cadmium, steel and nickel, and exposure to diesel engine exhaust while working may also be risk factors.

Personal factors

Family history – You may be at slightly higher risk if a family member has been diagnosed with lung cancer.

Other conditions – Having another lung disease (e.g. lung fibrosis, chronic bronchitis, pulmonary tuberculosis, emphysema) or human immunodeficiency virus (HIV) may increase the risk of lung cancer.

Older age – Lung cancer is diagnosed mostly in people aged over 60 years, although it can occur in younger people.

Who gets lung cancer?

About 14,500 Australians are diagnosed with lung cancer each year. The average age at diagnosis is around 72 years. More men than women develop lung cancer, but since the early 1980s rates have been steadily decreasing among men and increasing among women.

→ READ MORE: Lung cancer symptoms