Causes of cancer

Many things, including genes and a number of external factors, can cause cancer. Learn more about what causes cancer.

What causes cancer?

Cancer is a disorder that can occur inside any cell in our body.

It is a mistake in the DNA—the genetic codes of our cells—that causes the cell to grow without control.

While cancer is a mistake at the genetic level of the cell, in up to 90% of cases this genetic mistake is not one that has been inherited; it is mostly the exposure to one or more carcinogens—cancer causing factors—during our lifetime that causes cancer to occur.

However, our inherited genes do still play a role in how likely we are to develop cancer if we are exposed to one or more carcinogens. So the development of cancer is dependent on both exposure to one or more carcinogens and our predisposition.

Carcinogens (cancer causing factors)        

Carcinogens are factors, which cause the DNA inside a cell to become altered, or ‘mutated’. However, in order for a mutation to cause cancer, the mutation must cause the cell to do two things:

  1. to grow without control
  2. to become immortal, which means the cell doesn't die when it's supposed to

Carcinogens can be physical, chemical or biological.

Physical mutagens           

Physical mutation of DNA can be caused by ionising radiation, ultraviolet radiation and by mineral fibres. These three mutagens act in very different ways.

  1. Ionising radiation literally punches holes in the DNA, breaking the correct genetic sequence. Ionising radiation can come from directly from X-rays and solar radiation (cosmic rays) and indirectly from radon gas.
  2. Ultraviolet radiation, which comes from the sun, causes mutations by causing certain portions of DNA to remain bound together (even when they shouldn’t). This causes mutations by causing misreading of the DNA.
  3. Certain natural mineral fibres like asbestos, because of their size, can cause damage directly to DNA resulting in carcinogenic mutations.

Chemical mutagens

In the case of chemical mutagens, mutation is caused by foreign molecules binding to a cell’s DNA, causing it to be ‘misread’. Examples of chemical mutagens are benzopyrene (found in cigarette smoke), vinyl chloride (found in the plastics industry), aflatoxin (found in certain moulds) and hetrocyclic amines (found in over-cooked foods).

Biological mutagens

Biological mutagens may be viral or bacterial. Viral mutagens may use a number of different complex mechanisms to cause a cell to become cancerous. Viruses that can be a risk factor for different cancers include the human papilloma virus (implicated in cervical cancer), the human T-cell lymphyocytic virus (implicated in lymphoma), and the hepatitis B virus (implicated in liver cancer). One known bacterial mutagen is helicobacter pylori (implicated in stomach cancer).

Call our National Cancer Helpline

Freephone 1800 200 700 to talk to a specialist cancer nurse
It's open Monday-Thursday from 9am to 7pm and Friday from 9am to 5pm