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Tests on your bowel cancer cells

After a doctor removes tissue or cancer from your bowel, they send a sample of cells to the laboratory. A doctor called a pathologist does various tests on the cells.

These tests can diagnose cancer and look for gene changes. Some of these tests can show how well particular treatments might work, such as targeted cancer drugs.

Finding the type of cancer

A pathologist looks at the cancer cells under a microscope to see which type and grade of bowel cancer you have.

Testing for gene changes

Your doctors might look to see if your bowel cancer cells have changes (mutations) in certain genes. They do this if you are diagnosed with bowel cancer that has spread (advanced bowel cancer).

What are genes?

Genes are coded messages that tell cells how to behave. They control how our bodies grow and develop. All cancers develop because something has gone wrong with one or more of the genes in a cell. A change in a gene is called a ‘fault’ or ‘mutation’.

Diagram of a chromosome in a cell

The tests

Doctors can do various tests. The results of each test can be useful in different ways. The tests can:

  • show which targeted drug treatments might work for your bowel cancer
  • help doctors find new ways of treating bowel cancer
  • help you and the doctors understand more about the cause of your cancer

RAS genes

The doctor might test your bowel cancer to look for changes (mutations) in a group of genes called RAS genes. Mutated RAS genes can cause cancer cells to grow and spread.

You might have:

  • a normal RAS gene, which is also known as RAS wild type
  • an abnormal RAS gene, which is known as a mutated RAS gene

Targeted cancer drugs such as cetuximab and panitumumab can work well for people with advanced bowel cancer who have a normal RAS gene (RAS wild type).

BRAF genes

The doctor might look to see if your bowel cancer cells have changes (mutations) in the BRAF gene. This gene makes a protein called BRAF which is involved in cell growth. A change to this gene can cause it to make an overactive BRAF protein. This makes cells grow and divide too fast.

You might have:

  • BRAF positive bowel cancer, which means there are changes in the BRAF gene
  • BRAF negative bowel cancer, which means you don’t have these changes

Doctors know that people with BRAF positive bowel cancer don't respond as well to treatment. Researchers have been looking at different ways of treating this type of bowel cancer. 

Microsatellite instability

A small number of bowel cancers have DNA changes called microsatellite instability. Your doctor might check your bowel cancer for this.

Microsatellites are short, repeating arrangements (sequences) of DNA inside cells. Every time a cell divides, it makes new copies of these DNA sequences.  Cells can correct any mistakes that happen in this process.

But if these repair processes are faulty, mistakes can happen when the cell divides causing changes in the new copies of DNA. Changes in the length of the new DNA sequence are called microsatellite instability. These changes can cause cells to grow abnormally.

Your doctor might describe your test results as:

  • microsatellite stable (MSS) – this means they didn’t see any instability
  • microsatellite instability low (MSI low) – this means they saw a low level of instability
  • microsatellite instability high (MSI high) – this means they saw a high level of instability

Your doctor can use the test results to help you decide whether to have further genetic tests. Further genetic tests can tell you whether there is an inherited cause for your bowel cancer.

What happens?

You might not need any extra tests. The doctor can sometimes do genetic tests on your bowel cancer cells that they removed during surgery or when you were first diagnosed.

But sometimes the doctor needs to take another sample of your bowel cancer cells. They can take a sample from your bowel, or from a secondary site if your cancer has spread. They will tell you more about this, and about what the test will involve. 

Last reviewed: 
28 Mar 2019
  • BRAF mutant colorectal cancer: prognosis. Treatment and new perspectives
    E Sanz Garcia and others
    Annals of Oncology, volume 28 (11) pages 2648 – 2657  November 2017

  • MSI testing and its role in the management of colorectal cancer
    H Kawakami and others
    Current treatment Options Oncology 2015 July 16 (7) 30

  • Metastatic Colorectal Cancer: ESMO Clinical Practice Guidelines 
    E Cutsem and others
    Annals of Oncology, 2014. Volume 25, Pages ii1-iii9

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