Cancer and carcinogens


Cells grow then divide by mitosis only when we need new ones – when we’re growing or need to replace old or damaged cells.

When a cell becomes cancerous, it begins to grow and divide uncontrollably. New cells are produced – even if the body does not need them.

A group of cancerous cells produces a growth called a tumour.

Types of tumour

There are two types of tumour - benign and malignant. The table shows the difference between the two types:

Type of tumourCharacteristics
BenignGrows slowly; usually grow within a membrane, so can easily be removed; does not invade other parts of the body
MalignantGrows quickly; invades neighbouring tissues and can spread to other parts of the body in the bloodstream; as the tumour grows, cancer cells detach and can form secondary tumours in other parts of the body - this is called metastasis.

The diagram shows how cancer cells can invade surrounding tissue:

This shows how cancer cells can invade surrounding tissue.

Cancer cells are undifferentiated – they do not carry out their normal function.

At some point, secondary tumours may develop.

Diagram of how the tumour secretes chemicals

Development of a tumour

What causes cancer?

There are genetic factors that increase the likelihood of developing some cancers.

Chemicals and other agents that can cause cancer are called carcinogens.

Carcinogens cause cancer by damaging DNA. Carcinogens cause mutations to 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.

Something that increases the likelihood of developing a disease is called a risk factor. There are several risk factors for various types of cancers including:

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
  • 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 at work:

  • exposure to ionising radiation increases the risk factor
  • exposure to chemical carcinogens

There are also genetic risk factors for some cancers.