When patients are diagnosed with lung cancer, most of these people die within one year of diagnosis, making it one of the leading causes of death in the USA.

The peak incidence of lung cancer occurs between the ages of 55 and 65 years. On top of this the overall incidence is increasing, doubling approximately every 15 years.

The anti-smoking efforts started 20 years ago seems to have resulted in a levelling of the incidence in males. Unfortunately, the increasing incidence of smoking among women is showing itself as an increasing incidence of lung cancer.

At diagnosis, only 20 percent of people will have the disease confined to the lungs. Twenty-five percent would have spread to nearby lymph nodes and 55 percent would have spread to other organs; this is known as metastatic cancer. In those people who have disease confined to the lungs, five-year survival is only 30 percent for men and 50 percent for women. These survival rates haven't changed much over the past 20 years in spite of new types of treatment.

What causes lung cancer?

Lung cancer is caused by smoking cigarettes. This is one of the few cases where the main cause of a disease can be so clearly shown. Statistically, there is a dose related relationship between lung cancer death rate and the total amount (often expressed as "cigarette pack years") of cigarettes smoked. A person smoking two packs per day for 20 years has 60 to 70 times the risk of dying of lung cancer than the non-smoker.

The chances of developing lung cancer decrease if you give up smoking, but may never return to the levels of someone who has never smoked. The increase in incidence of lung cancer among women is directly related to the rising numbers of women smoking.

Any carcinogenic effects of industrial pollutants and the natural background radiation are compounded by smoking.

There are uncommon cases of non-smokers having lung cancer. These people usually have a particular type of lung cancer known as adenocarcinoma.

The different types of lung cancer

All cancers are classified according to their cell type. This classification is recommended by the World Health Organisation, so they are standard around the world.

Ninety-five percent of lung cancers fall into four major cell types. These are squamous or epidermoid carcinoma, small cell (also called "oat cell") carcinoma, adenocarcinoma (including bronchioloalveolar), and large cell (also called large cell anaplastic) carcinoma.

These various cell types have different disease courses and responses to therapy, so it is very important that the correct classification is made at diagnosis. The treatment decision depends on distinguishing between the small cell and "non-small cell" cancers.

Symptoms

Symptoms come from the lung itself, from spread to the lymph nodes, from spread to more distant organs and from what are known as paraneoplastic syndromes. These latter are caused by the metabolic effects of the tumour on other parts of the body.

A changed cough is a common presenting symptom. Most smokers have a cough, so change is important. Coughing up blood is obviously a warning sign. There may be increasing shortness of breath, due to compression of the airways by tumour or involved lymph nodes. A general feeling of tiredness, with weight loss and loss of appetite often accompany these symptoms.

A small number of people have no symptoms and are picked up on routine chest X-ray for TB or pre-employment screening. Unfortunately, studies in the USA have not shown any real benefit from screening asymptomatic people who are at risk of developing lung cancer. This is because most people have distant spread when diagnosed, even when the cancer is detected very early.

Treatment

Treatment depends on cell type and how advanced the disease is. So once diagnosed, a number of different tests are performed. These vary between centres and around the world. A CT scan is usually done first, followed by mediastinoscopy (a technique to look at the tissue in between the lungs in the centre of the chest). If symptoms suggest involvement of other parts of the body, then specific investigations will be carried out accordingly.

"Non-small cell" cancers are divided into those that can be removed by surgery and those that are too far advanced for this. If the cancer is confined to the chest in those too far advanced for surgery, then high dose radiotherapy is used. Cancers which have spread beyond the chest wall will be treated with high dose radiotherapy to the section within the chest, and chemotherapy.

Small cell cancers are treated with radiotherapy and chemotherapy. They are generally not ammenable to surgery.

As in all cancers, one of the best measures of prognosis (how well the patient will do) is what is called "performance status". In essence, this refers to whether the patient is up and about, or unable to continue to perform normally. The scale measured ranges from normal activity to bedridden. Astonishingly, this is often a better measure of prognosis than the extent of disease. In other words, someone with very advanced disease can still be up and about and active, confounding the doctors by living much longer than predicted!

Where do we go from here?

Obviously, most programmes concerned with lung cancer concentrate on prevention ? stopping people from smoking and preventing people from starting to smoke.

However, lung cancer is a major cause of mortality in both the West and the developing world. Consequently, there is plenty of research into new types of treatment, aimed at curing, or at least increasing the quality of remaining life for those who contract the disease. This consists of well-developed clinical trials to test new forms of therapy. These often involve a number of world centres.