Lung cancer

Lung cancer begins when abnormal cells grow and multiply in an uncontrolled way in one or both of the lungs. Cancer that starts in the lungs is known as primary lung cancer. It can spread to other parts of the body such as the lymph nodes, brain, adrenal glands, liver and bones.

When cancer starts in another part of the body and spreads to the lungs, it is called secondary or metastatic cancer in the lung.

The information here is about primary lung cancer only.

Learn more about:

• The lungs
• Different types of lung cancer
• What causes lung cancer?
• Who gets lung cancer?

The lungs

The lungs are the main organs for breathing, and are part of the respiratory system. As well as the lungs, the respiratory system 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.

Lobes

The lungs look like two large, spongy cones. Each lung is made up of sections called lobes – the left lung has two lobes and the right lung has three.

Diaphragm 

The lungs rest on the diaphragm, which is a wide, thin muscle that helps with breathing.

Mediastinum 

The space between the two lungs is called the mediastinum. Several 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 structures that collect and destroy bacteria and viruses.

Pleura 

The lungs are covered by two layers of a thin sheet of tissue called the pleura, which is about as thick as plastic cling wrap. The inner layer (the visceral layer) lines the lung surface, and the outer layer (the parietal layer) lines the chest wall and diaphragm. The layers are separated by a film of fluid that lets them slide over each other.

This helps the lungs move smoothly against the chest wall when you breathe. The pleural cavity is the potential space between the two layers, but there is no space between them when the lungs are healthy.

The respiratory system

The different types of lung cancer

There are two main types of primary lung cancer. These are classified according to the type of cells affected.

Types of lung cancer

Other types of cancer can also affect the lung area, but are not considered lung cancer. These include tumours that start in the space between the lungs (mediastinum) or in the chest wall.

Pleural mesothelioma is a cancer that affects the covering of the lung (the pleura). It is different to lung cancer and is usually caused by exposure to asbestos.

For more on this, see Pleural mesothelioma.

What causes lung cancer?

The causes of lung cancer are not 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 developing the disease. Having these risk factors does not mean you will develop lung cancer, but if you are concerned about your risk, talk to your doctor.

Tobacco smoking

In Australia, about 90% of lung cancer cases in males and 65% in females are estimated to be a result of tobacco smoking. The earlier a person starts smoking, the longer they smoke and the more cigarettes they smoke, the higher the risk of developing lung cancer. However, about one-fifth (21%) of people who are diagnosed with lung cancer have never been smokers.

Second-hand smoking 

Breathing in other people’s tobacco smoke (passive or second-hand smoke) can cause lung cancer. Living with a smoker increases a non-smoker’s risk by 20−30%.

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, there is still asbestos in some older buildings and fences.

Exposure to other elements 

People exposed to radioactive gas (radon) in the workplace, such as uranium miners, have an increased risk of lung cancer. Contact with the processing of arsenic, cadmium, steel and nickel may also be a risk factor.

Family history 

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

Personal history 

Having another lung disease (e.g. lung fibrosis, chronic bronchitis, pulmonary tuberculosis, emphysema) or HIV infection may increase the risk of lung tumours.

Older age 

Lung cancer is most commonly diagnosed over the age of 60 years, though it can occur in younger people.

Who gets lung cancer?

Each year, about 11,500 Australians are diagnosed with lung cancer. The average age at diagnosis is 71. It is the fifth most common cancer in Australia and accounts for 9% of all cancers diagnosed. More men than women develop lung cancer. The risk of being diagnosed before the age of 85 is 1 in 13 for men and 1 in 21 for women.