Everyone’s body is made up of millions of cells. With this in mind, the body is continuously replacing cells that don’t work with new ones. When the body destroys a cell, one of the remaining good cells will divide into two to replace the old cell. Usually this process is controlled carefully so that the numbers of new cells made are only replacing the ones destroyed. 

However, sometimes the cell won’t respond to a signal from the body to tell it to stop dividing therefore, it will continue making more copies of itself which will form a lump called a tumour.

Tumours will grow uncontrollably and destroy tissues and spread further and this is called cancer.