In patients with lung cancer, abnormal cells develop in one or both lungs and grow in an uncontrolled way to form tumours.
These tumours can affect how the lungs usually work, which is to supply oxygen to the body through the bloodstream and remove carbon dioxide from the body.
How does lung cancer develop?
Lung cancer develops when cells in the lung grow abnormally to form a tumour.
Air that is breathed in the lungs flows through tubes called bronchi, which branch into smaller airways called bronchioles. These branches end in tiny sacs, called alveoli, where oxygen and carbon dioxide is exchanged.
Although lung cancer can develop in any part of the lung, most lung cancers begin in the cells that line these air passages (the bronchi) and the airway branches (alveoli or bronchioles) in the lung.
Lung cancer cells that remain within the lungs are classed as non-invasive lung cancer. When the tumour invades normal tissues in the lung, the tumour is considered to be malignant. The cells can also invade and multiply in nearby parts of the body, such as the chest wall or diaphragm, obtaining a new blood supply to continue tumour growth.
How does lung cancer spread?
Lung cancer cells can spread from the lungs to other parts of the body by breaking away from the lung cancer tumour, invading nearby normal lung tissue and travelling through blood vessels or lymph vessels to reach other parts of the body. This process is called metastasis.
The most common sites are the adrenal gland, bone, brain, liver or the other lung. Lung cancer that spreads from the lungs to other parts of the body is called metastatic, secondary or advanced lung cancer.
What causes lung cancer?
Abnormal cell growth in the lungs develops from a change in the cells’ DNA, called DNA mutations. DNA mutations in lung cancer cells can be inherited from family members, or they can be caused by the normal ageing process or through different environmental factors.
Patients who are cigarette smokers have the highest chance of developing lung cancer compared to non-smokers. The risk of lung cancer increases with the number of cigarettes smoked and the months or years spent smoking. Cigar smoking and pipe smoking has the same risks as cigarette smoke, and second hand and passive smoking can also have an increased risk for lung cancer.
Not all patients who develop lung cancer are smokers. Patients who have a non-smoking or smoking relative who has had lung cancer can inherit damaged DNA. Being aged 6o years old and over also increases the risk for being diagnosed with lung cancer.
Patients who are infected with HIV, have certain diseases of the lungs or are being treated with radiation therapy to the breast or chest may be at increased of risk of lung cancer.
Other known environmental risk factors for lung cancer include, exposure to asbestos fibres, nickel or soot in the workplace, living where there is air pollution and radiation exposure to radon gas.
What different types of lung cancer exist?
The most common type of lung cancer is called non-small cell lung cancer. Non-small cell lung cancers include, squamous cell carcinoma that starts in the cells that line the airways of the lungs, adenocarcinoma the most common type of non-small cell lung cancer starting the mucous-secreting lung cells or large cell carcinoma.
The other type of lung cancer is called small cell lung cancer, which usually starts in the bronchi, and grows and spreads to other parts of the body quickly.
Lung cancer that is made up of both these types is called mixed small cell/large cell cancer.
There are other types of lung cancer that occur less frequently in patients called lung carcinoid tumours. Most of these tumours grow slowly and rarely spread to other parts of the body.
Treating and preventing lung cancer
Constantly improving treatments are helping to gradually reduce rates of lung cancer globally. Treatment for lung cancer depends on the stage at the time of diagnosis, which includes the size of the tumour and if tumour has spread in the lung, the type of lung cancer, cancer gene mutations and the overall health of the patient.
Lung cancer treatment can include, surgery to remove part or the whole lobe of the lung, the entire lung or part of the lung airway (bronchus). Radiation therapy and chemotherapy are also treatment options for patients.
An emerging body of research is indicating that knowing a tumour’s genomic profile could be more important for successful treatment than knowing its location or size. As each tumour’s genomic profile is unique, this approach is often referred to as personalised or precision medicine.
Increased awareness of lung cancer risks, such as smoking, is helping patients reduce their risk of developing lung cancer. Quitting smoking and reducing exposure to passive tobacco smoke can significantly reduce patient risk for developing lung cancer, with the risk of lung cancer decreased after years of quitting.
Raising awareness of risks with smoking and environmental factors for lung cancer, encouraging patients to learn their family history, and referring at-risk patients for regular screening checks are all important preventative measures.