WHAT IS CANCER?
Cancer is not a single disease. It is a type of disease. There are over 200 different cancers, and each occurs in its own way. What they have in common is that they all start in the same way – with a change in the normal make-up of a cell. To understand how cancer is caused, it helps to know a little about what cells are and how they work.

We all begin life as a single cell. This is formed when an egg cell is fertilised by a sperm. The fertilised cell then begins to reproduce itself. It divides into two, then four, then eight ... and so on, until a human being is complete.

IN THE BEGINNING
But cell division doesn't stop there. Cells are constantly at work in our bodies, dividing and multiplying to repair damaged skin, maintain hair growth, and perform a hundred other everyday tasks.

TYPES OF CELLS IN THE BODY

There are many types of cells to do all the different jobs. Almost every cell has a control centre, the nucleus. This determines what type of cell it is and also controls cell division. When a cell needs to divide – to repair a cut in your skin, for instance – it is the nucleus which controls the process.

Usually the instructions given by the nucleus are understood correctly. But sometimes things can go wrong, resulting abnormal cell. This cell then divides and produces a abnormal cell, then four, then eight ...

WHEN SOMETHING GOES WRONG
The division of normal cells is carefully controlled. But abnormal cells divide in an uncontrolled manner, and seem not to know when to stop.

A cluster of abnormal cells is called a tumour of primary growth. Not all tumours are cancers, however, there a types of tumours – benign and malignant.

Benign tumours are not cancers. They usually don’t need treatment. But if they do they can be removed by simple surgery.

It's the malignant ones that can be dangerous; they're the cancers. Malignant tumours can invade nearby parts of the body and may stop the cells there from working properly. Also cells, from malignant tumours can break away and travel – through the bloodstream, for instance – to other parts of the body. There they settle, forming new colonies of abnormal cells. These are called secondary growths.

The whole process is known as metastasis. Metastasis is one of the main features of cancer. It also makes it more dangerous. Most of lives lost of cancer occur because of the secondary growths. That's why it’s important to spot cancers early, before metastasis has happened.

This is the process which leads to cancer. But remember cancer is not a single disease. All cancers start like this, but what causes them in the first place, and how quickly they grow and spread, can be very different for each individual cancer.