Cell division by mitosis happens throughout the body. This normally occurs due to growth or because the body needs new cells to replace old or damaged cells. Genes in the nucleus tell cells when to start dividing and when to stop.
Cancer is a disease caused by changes in genes, which causes normal cells to change so that they grow and divide in an uncontrolled way. The uncontrolled growth causes a lump of cells, called a tumour, to form.
When a cell becomes cancerous, it begins to divide uncontrollably. New cells are produced even though the body does not need them.
The extra cells produced form growths called tumours. Most tumours are solid, but cancers of the blood, for example, leukaemia, are an exception.
There are two types of tumours:
Benign tumours typically grow within a membrane, so they can be easily removed. They do not invade other parts of the body and tend to grow slowly.
Malignant tumours grow rapidly. They invade neighbouring tissues and can spread to other parts of the body through the bloodstream.
As a malignant tumour grows and spreads, it can form smaller tumours, which are called secondary tumours. This process is known as metastasis.
We can inherit an increased risk of getting certain cancers, such as:
Carcinogens are substances that are capable of causing cancer. They can occur naturally in the environment (e.g. Ultraviolet radiation in sunlight). However, carcinogens can also be produced by humans, such as the exhaust fumes released by vehicles.
Some cancers are caused by lifestyle choices. For example: