A cancerous tumour that develops in the tissue of the lungs
Primary lung cancer, in which a tumour originates in lung tissue, is the third most common type of cancer in the UK (after skin cancer and breast cancer) and the leading cause of death due to cancer. In men, it is the most commonly diagnosed form of cancer after prostate cancer. In women, it comes third after breast and colorectal cancer, but causes more deaths than any other cancer. Lung cancer is about twice as common in men. It usually develops between the ages of 60 and 85. In the UK, there are about 39,000 new cases a year.
Smoking is by far the most important cause of lung cancer, and the prevalence of smoking is closely related to the incidence of the disease. In the UK, the levels of both smoking and lung cancer rose sharply in the first half of the 20th century. Smoking among men reached a peak around 1950, when more than 80 per cent of men smoked, and has since declined to about 22 per cent in 2007. In women, the number of smokers reached a high of 45 per cent in 1966 and has since declined to about 20 per cent in 2007. However, because lung cancer can take many years to develop, the effects of smoking can take 20 or 30 years to appear. Among men, the incidence of lung cancer peaked in the 1970s and then declined steadily. In women, the incidence of lung cancer increased slowly until the late 1990s and then levelled off.
The more cigarettes you smoke, the sooner you may develop cancer. For ex-ample, if you smoke 20 cigarettes a day, you may develop lung cancer after 20 years, but if you smoke 40 a day, you may develop the disease after only 10 years.
The type of cancer that develops depends on the type of cell in the lungs that becomes cancerous. Most lung cancers fall into one of four types: squamous cell carcinoma; adenocarcinoma; small cell carcinoma; and large cell carcinoma. Most of these cancers begin in the cells that line the bronchi, the airways that lead to the lungs.
Each type of cancer has a different growth pattern and response to treatment. In general terms, squamous cell carcinoma grows more slowly than the other types of lung cancer and spreads to other parts of the body late in the course of the disease. Small cell carcinoma is the most highly malignant (cancerous) type; this type of cancer grows rapidly and spreads very quickly throughout the body. Adenocarcinoma and large cell carcinoma both develop at a rate somewhere between that of squamous and small cell carcinomas.
Lung metastases are cancers that have spread to the lung from a tumour in another part of the body. Lung tissue is a common site for metastases because all circulating blood passes through the lungs, allowing cancerous cells to pass into lung tissue.
Smoking is the cause of lung cancer in approximately 90 per cent of cases. The more you smoke, the greater the risk of developing lung cancer. It is also more likely to develop in people who start smoking at a young age. For people who have never smoked, the risk of developing lung cancer is small, but it increases slightly for anyone who is exposed to other’s people’s tobacco smoke (passive smoking) on a regular basis.
Working with particular substances, such as radioactive materials, asbestos (see Asbestos-related diseases), chromium, and nickel, may lead to an increased risk of lung cancer, especially when the exposure is combined with smoking. Exposure to radon, a radioactive gas that is released slowly from granite rock, also leads to a slightly increased risk for people who live in areas that have a lot of granite. Living in an environment with a high level of air pollution may be a factor in some cases of lung cancer, but it is far less important as a cause than smoking. Other risk factors for lung cancer include a family history of the disease in a first-degree relative (parent or sibling); previous treatment for cancer, especially in smokers who have had radiotherapy to the chest and have continued to smoke; and reduced immunity, for example, due to HIV/AIDS or immunosuppressant drugs.
The symptoms of lung cancer depend on how far advanced the tumour is, but initial symptoms may include:
A new, persistent cough or change in a long-standing cough, sometimes with blood-streaked sputum.
Chest pain, which may be a dull ache, or a sharp pain that is worse on inhaling.
Shortness of breath.
Wheezing if the tumour is positioned so that it blocks an airway.
Abnormal curvature of the finger-nails, known as clubbing (see Nail abnormalities).
Some lung cancers do not produce any symptoms until they are advanced, when they may cause shortness of breath.
You should consult your doctor as soon as possible if you develop a new cough that is persistent, experience a change in a long-term cough, or develop any of the other symptoms associated with lung cancer listed here.
In some cases, pneumonia may develop in an area of the lung if an airway is blocked by a tumour. This may be the first indication of lung cancer. A tumour may also cause fluid to accumulate between the layers of the pleura, the thin membrane that separates the lungs from the wall of the chest (see Pleural effusion), which may lead to increased shortness of breath. Later, as the disease progresses, loss of appetite followed by weight loss and weakness may develop. A tumour at the top of the lung may affect the nerves that supply the arm, making the arm painful and weak. Small cell carcinomas may produce chemicals that mimic different hormones in the body and upset body chemistry as a result.
In addition, there may be symptoms from tumours that have spread from the lungs to other parts of the body. For example, headaches may result from cancer that has spread to the brain.
A chest X-ray is often one of the first investigations used when a person has a lung problem. A tumour is usually visible as a shadow on the X-ray.
Samples of sputum may be taken to look for cancerous cells, and your doctor may also perform a bronchoscopy to examine your airways. If a tumour is found during the procedure, a sample will be removed and examined under the microscope. If the tumour is cancerous, tests may be carried out to determine whether cancerous cells have spread to other parts of the body. In addition to blood tests, CT scanning and MRI of the brain, chest, and abdomen may be used to assess the extent of cancer spread. Radionuclide scanning may be performed to determine whether the cancer has spread to the bones.
Treatment of lung cancer depends on the type of cancer and whether it has spread to other parts of the body.
Surgery to remove a tumour in the lung is considered as an option only if the cancer has not spread. Surgery normally involves removal of a major part, or occasionally all, of the lung.
In 4 out of 5 cases, the cancer has already spread to other organs, and surgery is not an option. The size or location of the tumour or the presence of another serious disorder, such as chronic obstructive pulmonary disease may also make surgery inadvisable.
Small cell carcinoma is rarely treated with surgery because it is highly malignant and has usually spread beyond the lungs by the time it is diagnosed. This type of cancer is usually treated with chemotherapy. Radiotherapy may be used to treat metastases.
If a tumour cannot be removed surgically and is not a small cell carcinoma, chemotherapy is usually given initially. Although this does not destroy all cancerous cells, it does slow tumour growth. Radiotherapy may subsequently be given to alleviate specific problems, for example, to open up the airways to relieve breathlessness or to stop coughing up of blood.
The outlook is best for people whose cancer is detected early. Only about 1 in 20 people with lung cancer survives for 5 years or more after it is diagnosed. About 3 in 4 people who have surgery to remove a tumour survive for 2 years. People who have small cell carcinoma usually survive for 2–10 months after diagnosis. Surgery, radiotherapy, and chemotherapy may not prolong life in all cases, but they can alleviate symptoms and improve quality of life.
Lung cancer is closely linked to smoking. People who stop smoking greatly improve their chances of avoiding lung cancer, and long-term ex-smokers have only a slightly greater risk of developing lung cancer than nonsmokers.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.