Cancer is a disease that results from abnormal growth and division of cells that make up the body's tissues and organs.
Under normal circumstances, cells reproduce in an orderly fashion to replace old cells, maintain tissue health and repair injuries. However, when growth control is lost and cells divide too much and too fast, a cellular mass -or "tumour" -is formed.
If the tumour is confined to a few cell layers and it does not invade surrounding tissues or organs, it is considered benign. By contrast, if the tumour spreads to surrounding tissues or organs, it is considered malignant, or cancerous. In order to grow further, a cancer develops its own blood vessels and this process is called angiogenesis. When it first develops, a malignant tumour may be confined to its original site.
If cancerous cells are not treated they may break away from the original tumour, travel, and grow within other body parts, the process is known as metastasis.
Lung cancer is a growth of abnormal cells inside the lung. These cells reproduce at a much faster rate than normal cells. The abnormal cells stick together and form a cluster or growth, known as a tumour. If the abnormal cells began growing in the lung, this is known as a primary lung tumour.
Types of lung cancer
Depending on how the cells look under a microscope, cancers that begin in the lung are divided into 2 major types:
- Non-small cell lung cancer
- Small cell lung cancer
Non-small cell lung cancer generally spreads to other organs in the body at a slower rate than small cell lung cancer. Non-small cell lung cancer is the most common type of lung cancer, accounting for almost 80 per cent of lung cancers. Small cell lung cancer accounts for about 20 per cent of all lung cancers.
- Cigarette smoking is the major cause of lung cancer. Up to 90 per cent of cases of the disease are caused by smoking, and one in 10 smokers will develop lung cancer. The longer a person has been smoking and the more packs of cigarettes smoked per day, the greater the risk. However, it is not known why one smoker develops lung cancer while another does not.
- Research has also demonstrated the link between passive smoking and lung cancer.
- Workers exposed to industrial substances such as asbestos, nickel, chromium compounds, arsenic, polycyclic hydrocarbons and chloromethyl have a significantly high risk of developing lung cancer.
Lung cancer is very difficult to detect at an early stage. Common symptoms include:
- New or changing cough, along with hoarseness or shortness of breath or increased shortness of breath during exertion; and
- Recurring episodes of lung infection, weight loss and swelling of the face or arms.
Investigations to diagnose lung cancer include chest x-ray and CT scan. It is also necessary to determine whether there is any spread by obtaining a PET scan. Usually a biopsy will also be performed on the lump in the lung to confirm the diagnosis. It may also be necessary to biopsy some of the lymph nodes in the chest either using a camera with ultrasound in the airways (E-BUS) or surgically (mediastinoscopy).
The diagnosis and treatment of lung cancer involves a team of specialists including respiratory physicians, cardiothoracic surgeons, oncologists, radiation oncologists, radiologists and palliative care physicians. There are various treatment options available for lung cancer (with different aims), which include: surgery; chemotherapy; radiotherapy; and radiofrequency ablation.
Non-small cell lung cancers that are amenable to surgery are those where the cancer is confined to a lump in the lung or has only spread to the draining lymph nodes immediately next to the lump. When disease has spread to involve the lymph nodes in the centre of the chest or other organs, surgery alone is not effective and may not be indicated.
Surgery to treat lung cancer may involve removal of all the lung or part of the lung depending on the location of the tumour. For those cancers that have spread to the centre of the chest, a combined treatment approach may involve chemotherapy with radiotherapy possibly followed by surgery. Patients who present with widespread disease or later develop widespread non-small cell lung cancer may have chemotherapy which improves the chance of 12 months’ survival.
Radiotherapy is used to alleviate the symptoms from the primary cancer or other sites of disease spread, such as the bone.
Small cell lung cancer is primarily treated with chemotherapy. The best outcome is if the disease is confined to the chest but chemotherapy is still used in disease that is widespread at presentation. Radiotherapy may be used to consolidate the local chest area or to prevent metastases occurring in the brain. Radiotherapy can also be used for palliation of painful localized areas, such as in the bone.