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.

A diagram showing normal cell development in the body

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.

A diagram showing abnormal cell growth from Normal cell to Malignant tumour

The extra cells produced form growths called tumours. Most tumours are solid, but cancers of the blood, for example, leukaemia, are an exception.

Types of Tumours

There are two types of tumours:

1. Benign

2. Malignant

A diagram showing the two types of tumour; Benign and malignant tumour

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.

  • Benign tumours are not cancerous.

Malignant tumours grow rapidly. They invade neighbouring tissues and can spread to other parts of the body through the bloodstream.

Diagram showing a malignant tumours and how they spread over the body cells

  • Malignant cells are classified as cancer cells

As a malignant tumour grows and spreads, it can form smaller tumours, which are called secondary tumours. This process is known as metastasis.

Risk Factors

We can inherit an increased risk of getting certain cancers, such as:

  • Breast cancer
  • Colon cancer
  • Prostate cancer

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:

  • Carcinogens in cigarettes increase the risk of lung cancer
  • Exposure to ultraviolet (UV) radiation is linked to skin cancer
  • Alcohol consumption is linked to certain cancers