Cancer genomics

Genomics is the study of the body’s genes. Cancer develops because of changes in the genes. Understanding the cancer's genes can also be important when planning treatment.

What is cancer genomics?

Genomics is the study of genes. Cancer genomics looks at how genes are linked to cancer. This can help doctors:

  • understand how genes cause cancer to develop and grow
  • choose or develop new drugs that target a specific gene change in the cancer cells
  • plan a person’s treatment based on the genes of the cancer cells – this is called personalised medicine. It is sometimes called precision medicine.

Cells, chromosomes and genes

Our bodies are made up of tiny building blocks called cells. Inside nearly every cell is a set of genes. Genes are the instructions for your body to work. Genes carry instructions to make proteins. Proteins are messengers for the cell. They help the cell work properly.

Genes are made up of a chemical called deoxyribonucleic acid (DNA). DNA is made up of 4 chemicals called bases. The bases are arranged on 2 long strands that twist round each other like a rope. A gene is a short section of this rope.

Genes are organised into structures called chromosomes. Each chromosome is made up of many genes. Chromosomes are arranged in pairs. There are 23 pairs of chromosomes in the centre (nucleus) of nearly every cell in your body.

Your complete set of DNA is called your genome. Everyone’s DNA is made from the same 4 bases. But the way these are arranged is unique to you. Scientists can now look at the order of all the DNA in a cell and examine a person’s DNA. This is called whole genome sequencing.

DNA labelled

The diagram shows, in 3 linked illustrations, how a cell contains pairs of chromosomes, then how the chromosomes are made up of genes, and finally how the genes are made up of DNA. The left-hand illustration shows a cell. The cell contains a nucleus. In this are chromosomes, arranged into pairs. The middle illustration shows a close-up of a pair of chromosomes. These are made up of 2 vertical thread-like structures joined together in the middle to make an ‘H’ shape. The right-hand illustration shows the thread-like detail. It shows how, if unravelled, the genes are made up of DNA.


How do genes cause cancer?

If a gene changes, it may not give the correct instructions anymore. A change in a gene is called a gene variant or mutation.

Our cells can repair and correct some gene changes. But over time, gene variants in a cell may stop the cell working normally. Cancer may develop if cells like this multiply in an abnormal way and grow out of control.

Acquired gene variants

Gene variants can happen:

  • by chance, as a cell divides or does its job in the body
  • because of lifestyle – for example, diet or physical activity levels
  • because of things in a person's environment (environmental factors) – for example, sunlight or tobacco smoke.

These gene variants are called acquired gene variants. They only affect certain cells in the person’s body. They cannot be passed from a parent to child.

Inherited gene variants

A gene change that is passed from parent to child is called an inherited variant or mutation. This type of gene change is there from birth. It is in almost every cell in the person’s body for their whole life.

Some inherited gene variants cause a higher risk of certain types of cancer. The gene variant by itself does not cause cancer. But it may allow other damage to build up faster in cells. This increases the chance that cancer will develop.

Cancer cells and gene variants

Gene variants in a cancer cell can change the instructions for how the cell behaves. For example, the cell may:

  • make much more of a protein than is needed
  • make an abnormal protein which may make the cancer cells grow out of control
  • stop making a protein that usually repairs damage to cells.

Different cancers have different gene changes. This is called the genetic make-up of the cancer. Knowing about the genetic make-up of a cancer helps doctors:

  • understand what causes the cancer to develop and grow
  • choose or develop new drugs that target the specific gene change in the cancer cells
  • know what treatment is likely to be most effective.

People with the same type of cancer may have different gene changes in their cancer cells. This is why 1 person with a certain type of cancer will respond to a treatment, but another person with the same type of cancer may not respond to the same treatment.

Genes and cancer treatments

Knowing how genes are linked to cancer helps doctors develop and plan cancer treatments. For example, many cancer drugs are designed to target a specific gene change in a cancer cell. If your cancer cells carry a certain gene change, you may be offered a drug that targets this. This is called personalised medicine.

To find out whether a certain drug may be effective for your cancer, doctors send a sample of the cancer cells to a laboratory to be tested for specific gene changes. This is called genomic testing or molecular testing. It can also be called biomarker testing.

The NHS Genomics Medicine Service

The NHS Genomics Medicine Service was developed following the 100,000 Genomes Project. The project aimed to put in order (sequence) 100,000 genomes from about 85,000 people affected by a rare illness or cancer. The project was completed in 2018. Information from the project is helping researchers to develop new treatments and improve diagnosis.

The NHS Genomic Medicine Service is working to improve the diagnosis of cancers and rare diseases. Knowing more about the cancer can help doctors choose more effective treatments.

You can read more about the NHS Genomic Medicine Service to see how it aims to improve healthcare for people.

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Marc Tischkowitz, Reader and Honorary Consultant Physician in Medical Genetics.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 February 2023
Next review: 01 February 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.