Lynch Syndrome

Testing and Diagnosis

Because Lynch Syndrome is “silent” and without symptoms, until it causes cancer, most people who have it are unaware. Indeed, it is estimated that 95% of people with Lynch Syndrome are not aware they have it.7

The biggest sign that you could have Lynch Syndrome is your family’s medical history. If for example, several members of your family have been diagnosed with colorectal or endometrial cancer, particularly before the age of 50, then your doctor may advise testing for Lynch Syndrome.

If you have been diagnosed with colorectal or endometrial cancer yourself – especially below the age of 50 – then your doctor may also advise testing for Lynch Syndrome. European guidelines recommend that all patients with colorectal cancer are tested for Lynch Syndrome.5


The type of tests you will undergo for Lynch Syndrome will depend on whether you have already been diagnosed with cancer.

If you have been diagnosed with cancer, for example colorectal or endometrial cancer, a molecular screening test will probably be carried out on your tumour tissue to identify the likelihood of Lynch Syndrome. As you will have probably already had a biopsy (where some of the tissue of the tumour is removed) to confirm your diagnosis, you will not need to do anything else for this test.

There are two types of molecular screening tests for Lynch Syndrome:

  • Immunohistochemistry (IHC): A screening test for the proteins made by the MMR genes; if the genes are working properly, the proteins will be present. The absence of MMR proteins means an increased likelihood of Lynch Syndrome.
  • Microsatellite Instability (MSI): A DNA analysis test checks if the MMR genes are working properly by looking at the stability of parts of the DNA, called microsatellites. A high MSI status means a high likelihood of Lynch Syndrome.

After the molecular screening, you will have germline genetic testing to confirm the diagnosis. This involves a simple blood test, which will confirm if you have Lynch Syndrome or not. The result may take a few weeks.

If you have not been diagnosed with cancer, the first test you will have is the germline genetic testing.

Consent is needed before genetic testing, so it is likely your doctor will offer you genetic counselling with a specialist counsellor, who will talk you through the process and answer any questions you have.


It can be hard to hear a diagnosis confirmed, especially one that increases your risk of cancer. But having a clear diagnosis means it is possible to be vigilant and take action sooner than later.

If you are diagnosed with Lynch Syndrome, you will probably need to undergo regular cancer screening for the remainder of your life (beginning in adulthood) to detect cancer early, should it develop.

There are also some treatment approaches you could consider to prevent cancer, especially if you have a very strong family history of a certain cancer type. More information about this is below.

Talking To Family

One of your first considerations after being diagnosed with Lynch Syndrome will be about your family members. Because it is a hereditary condition, it is likely that some of your blood relatives – your parents, siblings, children, grandparents, aunts, uncles, nieces, nephews, and more distantly related family members – share the same genetic mutations.

It is important that you inform all your blood relatives about your diagnosis so that they might also consider genetic counselling and testing for the same gene mutation.

Remember, a faulty gene is nobody’s fault. It is a difficult conversation to have, but it is better that people have the information so that they can act on it.

For those with children, if one parent is a carrier of Lynch Syndrome, then there is a 50% chance that each child will have the genes that cause Lynch Syndrome. Genetic testing is generally not recommended for children below 18 – there is no preventative treatment or screening that is recommended for children, and it is extremely rare for these cancers to occur at such a young age. So, it is generally recommended to wait until your children reach adulthood, at which point they can decide whether to have the genetic test.

5. Stjepanovic N, Moreira L, Carneiro F, et al. ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol (2019); 00: 1–34.
7. Bowel Cancer UK. Testing for Lynch Syndrome – what you need to know. Available from:,t%20know%20they%20have%20it.

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