What is lung cancer?

Lung cancer begins when abnormal cells grow and multiply in an uncontrolled way in one or both 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 lungs

The lungs are the main organs for breathing and 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 and small airways called bronchioles.

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. The lungs rest on the diaphragm, which is a wide, thin muscle that helps with breathing. The space between the two lungs is called the mediastinum. 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. 
 

How breathing works

When you breathe in (inhale), air goes into the nose or mouth, down the trachea and into the bronchi and bronchioles. At the end of the bronchioles, tiny air sacs called alveoli pass oxygen into the blood and collect the waste gas (carbon dioxide). When you breathe out (exhale), carbon dioxide is removed from the body and released back into the atmosphere.

Types of lung cancer

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

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.

Non-small cell lung cancer (NSCLC)

NSCLC makes up about 85% of lung cancers. It may be classified as:

• adenocarcinoma – begins in mucus-producing cells, more often found in the outer part of the lungs.
• squamous cell carcinoma – begins in thin, flat cells, most often found in the larger airways.
• large cell undifferentiated carcinoma – the cancer cells are not clearly squamous or adenocarcinoma.

Small cell lung cancer (SCLC)

SCLC makes up about 15% of lung cancers. It tends to start in the middle of the lungs, and usually spreads more quickly than NSCLC.

Risk factors

A risk factor is anything that is known to increase a person’s chances of developing a certain condition, such as cancer. Not all causes of lung cancer are fully understood, and some people develop lung cancer without having any known risk factors.  

• 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 in five people (21%) 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 up to 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. Air pollution, contact with the processing of arsenic, cadmium, steel and nickel, and exposure to diesel in the workplace may also be risk factors.
• 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 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.

Symptoms

The main symptoms of lung cancer are:

• a persistent new cough lasting more than three weeks or a change in a cough you've had for a long time
• breathlessness
• chest and/or shoulder pain
• a chest infection that lasts more than three weeks or that keeps coming back. 
• coughing or spitting up blood.

Other symptoms include fatigue, weight loss, hoarse voice, wheezing, difficulty swallowing, abdominal or joint pain, and enlarged fingertips (finger clubbing). Having any one of these symptoms does not necessarily mean that you have lung cancer. Some of these symptoms may be caused by other conditions or from the side effects of smoking. However, if you have symptoms, you should see your doctor without delay.

Lung cancer symptoms can be vague and the disease is often discovered when it has spread to other parts of the body. Sometimes, there are no symptoms and the cancer is found during routine tests (often an x-ray or CT scan) for other conditions.

Health professionals

Your general practitioner (GP) will organise the first tests to assess your symptoms. If these tests do not rule out cancer, you will usually be referred to a respiratory physician, who will arrange further tests. If lung cancer is diagnosed, the specialist will consider treatment options. Often these will be discussed with other health professionals at what is known as a multidisciplinary team (MDT) meeting.

During and after treatment you will see a range of health professionals, which may include a thoracic surgeon, medical oncologist, dietician and psychologist, who specialise in different aspects of your care. The health professionals you see will depend on whether the lung cancer has spread.