What is it?
Cancer is not a single disease. It's a family of about 200, affecting different parts of the body. A carcinogen or 'cancer-trigger' interacts with DNA (the internal genetic code of cells) in normal cells, setting off a process called carcinogenesis. Mutant cells then reproduce at an abnormally rapid rate. Cancer cells usually group together in tumours and if their growth is not stopped or slowed they 'metastasize' or spread to other parts of the body. Most cancers kill when these secondary tumours impair some vital body organ such as the brain or liver.

How do you get it?
Carcinogens come from a number of different sources both natural and synthetic. It is a matter of hot debate which is more important. However it is clear you can get cancer from both your living habits (smoking, excess drinking, or too many fatty, smoked or salted foods) as well as from the environment - either on the job or in your community. Radiation from natural sources like sunlight and radon gas can also be carcinogenic. This natural background radiation is aggravated by radioactivity from uranium mining, atomic wastes or even going to a tanning clinic. A wide range of industrially-produced chemicals are known to be carcinogenic - including asbestos, benzene and vinyl chloride. Many other chemicals (including widely-used commercial pesticides) are also suspected carcinogens. Workers using these chemicals are in most danger, although consumers can be exposed too - by pesticides on fresh fruit and vegetables for example. The dosage of any particular chemical needed to cause a cancer is a point of dispute among cancer researchers.

What isn't known?
No one knows exactly what cancer is yet. Some say ills connected to weaknesses in the immune system: others connect some cancers to viruses. Whether you can inherit a genetic tendency to cancer is a matter of much debate. Recently researchers have identified cancer-causing genes called 'oncogenes'. These are activated by a little-understood biological process that is set off by a cancer-trigger. When this occurs other genes (known as tumour-suppressor genes) cease to operate properly. The oncogenes then set off uncontrolled growth of cancer cells. Even less is known about how to prevent, stop or slow down this growth once it is set in motion. And this is essential if the much-searched-for cure for cancer is to become a reality.

What happens to you?
The progress of a cancer varies from person to person, but the physiological process has some basic similarities. Abnormal cancer cells subdivide, forming a primary tumour (except in blood cancers like leukemia) and either spread to neighbouring parts of the body or break off and move to more distant locations through the body's blood stream or lymphatic system. First symptoms may include; change in bowel or bladder habits; persistent sore throat or nagging cough; unusual bleeding or discharge: thickening or lumps in breast, testicles or elsewhere; persistent indigestion or difficulty in swallowing; obvious change in size or bleeding of a mole. For some cancers, early detection increases the survival rate quite dramatically.

How do I avoid cancer?
Prevention is the best precaution. There are no absolute guarantees but you can improve your chances of not getting cancer by careful attention to diet, by not smoking and by drinking only moderate amounts of alcohol. Avoid dangerous chemicals and be conscious of threats to the environment as well as dangerous consumer products like pesticides and pharmaceuticals.

Who gets it?
Cancer is a chronic disease which affects a wide cross-section of people. Habits like smoking, chewing betel nut mixed with tobacco (a common Asian practice), eating fatty food or a lot of smoked fish and meat, make people more susceptible. It is also possible to inherit a tendency to get particular cancers like breast cancer. Epidemiologists have found higher cancer rates in certain occupations like asbestos mining and in heavily-industrialized and polluted areas such as the Los Angeles basin or greater Shanghai. The Cape Breton region of Canada has a cancer rate 150 per cent higher than the rest of the country. This is probably linked to the production of industrial coke and coal tar in the area. Regions with older 'smokestack' industries like Scotland have some of the world's highest lung cancer rates. Clusters of cancers have been found in the US around nuclear weapons factories. There is growing concern that pesticides dumped in the Third World will contribute to cancers among farm workers and consumers. Despite its reputation as a disease of affluent society more than half of cancers occur in the Third World where people are more susceptible due to malnutrition and weakened immune systems.

What can you do when you have it?
Some skin cancers can be treated effectively. But for most other cancers there is no sure-fire treatment. Millions have been spent to find a 'magic bullet' cure for cancer with only marginal results. Doctors believe in removing a cancerous tumour wherever possible, before it has time to spread. But this need not entail extensive surgery. Make sure you know the surgical options before you agree to the knife. Other forms of treatment such as radiation therapy (targeted doses of high-energy rays to destroy tumours) or chemotherapy (doses of chemicals to slow down cancerous cell reproduction) are more controversial. Many critics charge that these techniques (particularly chemotherapy) are overused and that toxic side-effects may outweigh benefits. However there have been some good results using chemotherapy to treat leukemia (blood cancer) in children and in breast and testicular cancer. Alternative therapies to increase individual resistance include relaxation, diet, heavy use of vitamins and hypnosis.

What is being done about it?
Cancer is big business. Medical costs of treatment are sky-high - $13 billion in the US in 1980. Billions more have been spent trying to find a cancer cure. In 1986 alone in the US $2.2 billion was spent on research. Thousands of people are funded or employed by national cancer societies and para-government research agencies. Although there is much official optimism about a big scientific breakthrough there has been very little actual progress over the past couple of decades. And remarkably little money has been spent on preventing cancers - either by test screening, education campaigns or organizing against industrially produced carcinogens.