Cancer and carcinogens


When a person is growing or replacing old and damaged cells, new cells are produced by mitosis.

Sometimes, cells begin to divide uncontrollably. New cells are produced – even if the body does not need them. This produces a growth called a tumour.

Types of tumour

There are two types of tumour – benign and malignant:

Type of tumourCharacteristics
BenignNormally grow slowly
BenignUsually grow within a membrane, so can easily be removed and in most cases do not grow back
BenignDo not spread to other parts of the body
BenignCan still be life-threatening if they cause damage to an organ
MalignantAre cancerous
MalignantNormally grow quickly
MalignantCan spread to other parts of the body in the bloodstream
MalignantAs the tumour grows, cancer cells detach and can form secondary tumours in other parts of the body - this is called metastasis

The diagrams shows how cancer cells can invade surrounding tissue:

This shows how cancer cells can invade surrounding tissue.Image shows how malignant cells can divide and invade normal cells.
Diagram of how the tumour secretes chemicals

Development of a tumour

What causes cancer?

Something that increases the likelihood of developing a disease is called a risk factor. Chemicals and other agents that can cause cancer are called carcinogens.

Carcinogens cause cancer by damaging DNA. Carcinogens increase the chance that mutations will occur. A single mutation will not cause cancer – several are required. For this reason, we are more likely to develop cancer as we get older. There are several risk factors for various types of cancers.

Genetic factors

There are genetic risk factors that increase the likelihood of developing some cancers. For example, inheriting a mutation in the BRCA1 gene can increase a person's risk of developing breast cancer.

Lifestyle factors

  • Viruses linked with cancer, such as the human papilloma virus (HPV), being spread from person to person through sexual intercourse.
  • The chemical carcinogens in cigarette smoke increasing the risk of lung cancer.
  • Alcohol intake is linked with certain cancers, such as liver cancer.
  • Exposure to ultraviolet radiation, part of which is ionising, during sunbathing or outdoor activities, leading to the development of skin cancers.
  • Diet, including fat and salt intake, increases the risk of cancer.

Industrial and environmental factors

  • Exposure to ionising radiation such as UV radiation from sunlight.
  • Exposure to chemical carcinogens. An example is asbestos.