What is lung cancer?
Lung cancer is a malignant tumour that grows 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.
Sometimes a cancer starts in another part of the body and spreads to the lungs. This is known as secondary or metastatic cancer in the lung.
The information here is about primary lung cancer only.
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Who gets lung cancer?
Each year, about 11,000 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 close to 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 22 for women.
What are the different types of lung cancer?
There are several types of primary lung cancer, which are classified according to the type of cells affected, and a number of less common subtypes. Cancers are named for the way the cells appear when viewed under a microscope.
Non-small cell lung cancer (NSCLC)
This type accounts for up over 80% of lung cancers. NSCLC may be classified as:
- adenocarcinoma (begins in mucus-producing cells and is more often found in the outer part of the lungs)
- squamous cell carcinoma (most commonly develops in the larger airways)
- large cell undifferentiated carcinoma (the cancer cells are not clearly squamous or adenocarcinoma)
Small cell lung cancer (SCLC)
Makes up about 15–20% of lung cancers. SCLC tends to start in the middle of the lungs, and usually spreads more quickly than NSCLC.
Other tumours starting in the space between the lungs (mediastinum) or chest wall
Thymus gland tumours, germ cell tumours, tumours of nerve tissue and lymph gland tumours (lymphoma) can arise in the mediastinum. These are not strictly lung cancer.
Primary tumours of bone, cartilage or muscle can also arise in the chest wall but these are rare.
A type of cancer that affects the covering of the lung (the pleura). It is different to lung cancer. There are two main types of mesothelioma: pleural and peritoneal. In most cases, exposure to asbestos is the only known cause of pleural mesothelioma.
What causes lung cancer?
While the causes of lung cancer are not fully understood, a number of risk factors are associated with developing the disease. These include:
Smoking causes almost 9 out of 10 lung cancers. Compared with nonsmokers, smokers are 25 times more likely to develop lung cancer. In Australia, about 84% of lung cancer cases in males, and 74% in females, are estimated to be a result of tobacco smoking.
The risk of developing lung cancer is strongly linked to the age a person starts smoking, how long they smoke and the number of cigarettes they smoke.
Breathing in other people’s tobacco smoke (passive or second-hand smoke) can cause lung cancer.
People who have never smoked but who have been frequently exposed to second-hand smoke are 20–30% more likely to develop lung cancer than nonsmokers who have not been exposed. People who have never smoked and have not been around second-hand smoke have about a 0.5% risk of developing lung cancer.
Exposure to asbestos
People who are exposed to asbestos have a greater risk of developing cancer, particularly pleural mesothelioma.
Although the use of asbestos in building materials has been banned nationally since 2003, it may still be in some older buildings. People who have been exposed to asbestos and are, or have been, a smoker are at even greater risk.
It can take many years after being exposed to asbestos for mesothelioma to develop. This is called the latency period or latent interval, and it is usually between 20 and 60 years.
Exposure to other elements
Contact with the processing of steel, nickel, chrome and coal gas may be a risk factor. Exposure to radiation and other air pollution, such as diesel particulate matter, also increases the risk of lung cancer.
Having a family member diagnosed with lung cancer increases the risk.
The risk of developing lung cancer is increased if you have been previously diagnosed with another lung disease such as lung fibrosis, chronic bronchitis, emphysema or pulmonary tuberculosis.
Lung cancer is most commonly diagnosed in people aged 60 years and older, though it can occur in younger people.
If you are concerned about any of these risk factors, talk to your doctor.
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, windpipe (trachea), and airways (tubes) to each lung. These consist of large airways known as bronchi (singular: bronchus) 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. A number of structures lie in this space, including:
- the heart and large blood vessels
- the windpipe (trachea) – the tube that carries air into lungs
- the oesophagus – the tube that carries food from the mouth to the stomach
- lymph nodes – bean-shaped structures that collect lymph fluid and foreign matter from the lungs.
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) is attached to the lungs, and the outer layer (the parietal layer) lines the chest wall and diaphragm.
Between the two layers is the pleural cavity (also called pleural space), which normally contains a small amount of fluid. This fluid allows the two layers of pleura to slide over each other so the lungs move smoothly against the chest wall when you breathe.
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.