Globally, more cases of lung cancer are diagnosed every year than any other single type of cancer. Around 1.6 million people were told they had the disease in 2009. In the UK, more men are confirmed as having lung cancer than are diagnosed with prostate cancer. Lung cancer and breast cancer rates in women are very similar, with lung cancer rates decreasing slightly in recent years. In both sexes, lung cancer is responsible for six in every 100 deaths of any cause, and for 22%of all deaths due to cancer.
Primary lung cancer and secondary lung cancer
Primary lung cancer is defined as a malignant cancer that originates in the lungs. It is usually caused by smoking.
Secondary lung cancer is a malignant cancer that grows in the lungs but has spread there through the process of metastasis. Cancerous cells from an original tumour elsewhere in the body – perhaps the breast, the prostate or the skin – travel in the blood or lymph system and set up new tumours in the lung.
For both types, early diagnosis is vital if treatment is to be successful. This article focuses on primary lung cancer, although the treatment for primary and secondary disease can be similar.
Types of primary lung cancer
The most common form of primary lung cancer is non-small cell cancer. More than four in every five people diagnosed with lung cancer have this type. The rest are classified as small cell cancers. Although these are rarer, they can be faster growing and more aggressive, and therefore more difficult to treat.
What causes primary lung cancer?
Around 85% of people who develop primary lung cancer do so due to the effects of smoking tobacco. Other causes include being exposed to air pollution (specifically radon gas), industrial pollutants (specifically asbestos), having a genetic condition that makes you more likely to develop cancers of all types, and passive smoking.
Cigarette smoke has been found to contain around 4000 potentially carcinogenic substances. The two main ones are the polycyclic aromatic hydrocarbons and nitrosamines produced when tobacco burns. Nicotine itself is not thought to be carcinogenic, but it paralyses the tiny hairs (cilia) that allow the lungs to expel other irritants, allowing the carcinogenic chemicals to have more time to damage cells.
Estimating lung cancer risk
The risk of developing primary lung cancer is directly proportional to the amount you have smoked over a long period. One calculation that can give an idea of risk is to multiply the number of packs of 20 cigarettes that you smoke on average every day by the number of years you have been smoking. The higher the score, the greater your risk. One study estimated that people who smoke two packs a day for at least five years have a one in seven chance of developing lung cancer. This risk reduces gradually if you stop smoking, returning to the normal level after ten years of not smoking.
Why primary lung cancer is often diagnosed too late
Deaths from lung cancer are high because it is often recognised only when it has become quite advanced. Early stage lung cancer causes few definite symptoms, so people need to be more aware that any of the following signs should be checked out by a GP:
A cough that just won’t go away: some viral coughs last for weeks and several non-cancerous chronic lung diseases cause a long-term chronic cough. Any cough that lasts more than six to eight weeks needs to be investigated
A cough that changes: if you have emphysema or bouts of bronchitis, you may have a persistent cough, but any change in the cough warrants attention
Having a hoarse voice: not being able to speak properly when there is no problem with your throat can be an early warning sign
Loss of weight for no apparent reason: if your weight starts to fall and you have not been dieting, the underlying cause needs to be identified
Feeling short of breath when resting: this can be caused by other lung conditions, but it is important to rule out lung cancer
Pain in the chest or blood in the sputum: pain that is worse when you breathe more deeply or coughing up even a small amount of blood are both worrying signs.
When lung cancer has started to spread it can cause all sorts of symptoms unrelated to breathing and lung function. These symptoms are diverse and depend on where the cancer has spread to.
Tests used to diagnose lung cancer
The early symptoms of primary lung cancer are non-specific, which means they can be caused by conditions other than cancer, for example tuberculosis. Primary lung cancer is usually confirmed by an X-ray or CT scan, followed by confirmation via a biopsy, in which a small sample of tissue is examined under the microscope. The same tests are used to diagnose secondary lung cancer.
A lung biopsy is performed by bronchoscopy in which a flexible camera with assorted tools is passed down the trachea. This device is guided to the site of the suspected tumour using ultrasound and a small piece of tissue is then cut off and removed for analysis.
Treatment for lung cancer
Individual treatment plans depend on whether someone has primary or secondary lung cancer, the type of lung cancer (small cell or non-small cell) they have and how advanced the cancer has become. The main treatments include:
An operation to remove the tumour: if the cancer is small and localised, the tumour and a margin of healthy tissue are cut away. Lung function is taken over by the remaining lung tissue and this can lead to a complete remission
Radiotherapy: this can be used as a followup treatment to surgery to prevent the lung cancer coming back, or it can be used to tackle lung tumours that are large or widespread in the lungs. Radiotherapy is often used to treat secondary lung cancer, as this may involve several tumours
Chemotherapy: drugs injected into the body kill rapidly dividing cells. This includes the cancer cells but also normal cells, which is why chemotherapy can have side effects that are difficult to cope with
New, more specific therapies: cancer research is developing specific biological treatments for many cancers, including lung cancer. Erlotinib (Tarceva®) and Gefitinib (Iressa®) are two specific treatments that are used to treat patients with non-small cell lung cancer. Cetuximab, a monoclonal antibody therapy, can also be used.