All Get Prepared

Cancer happens when our genes go through changes that can't be fixed.1

Genes are specific parts of our DNA that are involved in making proteins. They carry the coded recipe for how each cell in your body should work. This includes how to behave, when to grow and make new cells, and when to die.1,2

What causes changes to our DNA and genes? 

Changes in the DNA of a cell are called mutations. These may be caused by:1,3

  1. Mistakes during cell division
    • Our cells naturally divide to make new cells; when this happens, the original cell makes a copy of its DNA for the new cell.
    • Sometimes mistakes can happen in the copying process and the new cell contains damaged DNA
  2. Through coming into contact with DNA damaging agents
    • Coming into contact with DNA-damaging agents - such as cigarette smoke, ultraviolet radiation from the sun, or certain foods or chemicals - may cause changes to our DNA
  3. Inherited from parents
    • Since our DNA is passed down to us from our parents, it's possible for genetic mutations to also be passed down (known as inherited mutations)

But not all mutations cause cancer. Some genetic changes go unnoticed as the body does what it can to fix or remove any damaged DNA in the body.2

How are genes involved in cancer? 

There are four main types of gene that, if affected, can go on to cause cancer. These include:1

Oncogenes1

Comparison of a normal oncogene and a mutated oncogene. Normal oncogenes tell cells when to grow and divide to make new cells, switching on and off as needed. When an oncogene is damaged and becomes permanently switched on, cells continue to divide out of control, which may lead to cancer.

Tumour suppressor genes1

Illustration comparing normal tumour suppressor genes and mutated tumour suppressor genes. Normal tumour suppressor genes tell cells to slow down their growth and stop multiplying, helping to keep cell division under control. When a cell is damaged, these genes are helpful as they stop it making more cells that carry the same damage. When tumour suppressor genes are turned off or faulty, they don't work; so faulty cells are allowed to multiply out of control and this may cause cancer.

DNA repair genes1

Most DNA damage in our bodies is unnoticed because of DNA repair genes, which repair errors that have been found in our DNA. 

Illustration showing DNA repair. Damaged DNA is repaired, and errors do not build up

 

But when the DNA repair genes are damaged, the faulty cells can’t be fixed; they are allowed to grow and multiply, which allows errors to build up and may lead to cancer.

 

Illustration showing DNA repair. Damaged DNA is repaired, and errors do not build up

Cell self-destruct genes1

These are genes that tell cells to die if they become too old or damaged.

Illustration showing an undamaged self-destruct gene. The cell death gene is ON, and therefore old and damaged cells die.

 

But if these genes are damaged, they can’t send signals to the old or damaged cells; they are allowed to survive in the body and may become cancerous.

 

Illustration showing an undamaged self-destruct gene. The cell death gene is ON, and therefore old and damaged cells die.

There’s a lot to understand when thinking about where cancer comes from. Here we’ve shared the basics of what cancer is and how changes in genes (known as mutations) can cause cancer. Explore the site menu to learn more about different types of cancer and navigating life after a diagnosis.

References

  1. Cancer Research UK. Genes, DNA and Cancer. Available at: https://www.cancerresearchuk.org/about-cancer/what-is-cancer/genes-dna-and-cancer [Accessed May 2026].
  2. National Institutes of Health, National Human Genome Research Institute. Deoxyribonucleic Acid (DNA) Fact Sheet. Available at: www.genome.gov/about-genomics/fact-sheets/Deoxyribonucleic-Acid-Fact-Sheet [Accessed May 2026].
  3. National Institutes of Health, National Cancer Institute. Mutation. Available at: www.cancer.gov/publications/dictionaries/cancer-terms/def/mutation [Accessed May 2026].