People get cancer when cells within their bodies divide without control or order. The body is made up of many types of cells, and it is normal for them to grow, divide and produce more cells when the body needs them. Cancer occurs when cells keep dividing, even when new cells are not needed. The mass of extra cells may produce a tumor that can be:

  • Benign (not cancer)
    Benign tumors are rarely life-threatening, and they do not spread to other parts of the body. They often can be removed and usually do not grow back.
  • Malignant (cancer)
    Malignant tumors can invade, damage and destroy nearby tissues and spread to other parts of the body.

Your body is made up of billions of cells that can only be seen under a microscope. These cells are grouped together to make up the tissues and organs of our bodies. They are a bit like building blocks. Different types of body tissues are made up of different types of body cells. For example, there are bone cells in bone and breast cells in the breast.

Different types of cells in the body do different jobs. They all have a center called a nucleus. Inside the nucleus are the genes. Genes are really bits of code and control the cell. They decide when it will reproduce, what it does and even when it will die.

Normally the genes make sure that cells grow and reproduce in an orderly and controlled way. If the system goes wrong for any reason, the usual result is that the cell dies. Rarely, the system goes wrong in a way that allows a cell to keep on dividing until a lump called a ‘tumour’ is formed.

It is the ability to spread that makes a cancer harmful. If a cancer is not treated, it can spread into the organs near to where it started growing. It can also damage other parts of the body that it spreads to.

The place where a cancer begins is called the ‘primary cancer’. Cancers may also spread into nearby body tissues. For example ovarian cancer can spread to the lining of the abdomen (the peritoneum). This is called locally advanced cancer.

Cancer cells can break away from the primary tumour and be carried in the blood or lymphatic system to other parts of the body. There they can start to grow into new tumours. Tumours from cancers that have spread are called ‘secondary cancers’ or ‘metastases’