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Lynch Syndrome information for patients

This information has been developed for individuals who have recently been diagnosed with colorectal (bowel) or endometrial (womb) cancer and have been invited for a genetic assessment and possible genetic testing for Lynch syndrome. This is because initial testing of their cancer (tumour) suggests it might have been caused by an inherited condition called Lynch syndrome.

You might have been provided with an information leaflet about your genetics appointment. The information on these pages was developed to provide further detail and may answer most of the questions that you might have about your appointment, or other questions that you might have after your appointment.

It covers the following:

The information on this page is intended to help people who have questions about why they have been referred to genetics, or about the initial tests done on their cancer (tumour). You can also go directly to the sections above that you would like to read more about.

Do I have an inherited condition?

In the majority of cases, colorectal and endometrial cancers are not inherited conditions. In the case of colorectal cancer, it is common in the general population, affecting 1 in 14 men and 1 in 19 women at some point during their life, more commonly after the age of 60.

Most cancers occur sporadically or ‘out of the blue’. However, in about 5-10% (5-10 in 100) of the individuals who develop colorectal or endometrial cancer, cancer is caused by a genetic alteration (a change in their genetic code instructions, or what we are going to call a ‘genetic change’). In about 3% (3 in 100) of all colorectal or endometrial cancers, the genes affected are those whose task is to repair abnormalities when cells are made.

These repair genes (called DNA mismatch repair genes) protect us from developing certain cancer types. This is the case in Lynch syndrome, which is the most common cause of inherited colon and endometrial cancer. It affects 1 in 278 people.

How is Lynch syndrome diagnosed?

It is not straightforward to find out if a cancer is inherited or sporadic (out of the blue). To find out if someone has an inherited cancer that is being passed down in the family, there are different tests that need to be performed. In addition to taking a detailed family history, for Lynch syndrome, some tests are performed on the cancer (tumour) sample. This is because Lynch syndrome leaves a fingerprint in the tumour.

The initial tumour tests are immunochemistry (IHC) and microsatellite instability (MSI):

  • Immunochemistry (IHC). Every person diagnosed with colorectal or endometrial cancer has IHC performed on their tumour. IHC looks at the expression of the proteins produced by these ‘mismatch repair’ genes. If there is a loss of expression of any of these proteins, you may be offered genetic testing to find out if you have Lynch syndrome.
  • Microsatellite Instability (MSI). This is another type of genetic test on the tumour to find out if you are likely to have Lynch syndrome. If the result is positive, you might have Lynch syndrome, and you will be offered genetic testing.

Additional testing may be required using MLH1 promoter Hypermethylation (MLH1 Methylation). In some cases, following an IHC test, this test might be necessary to clarify if the cancer is sporadic and originates in the tumour cells, or if it could possibly be inherited. If the result of this test shows that the tumour sample is methylated, it clarifies that the cancer is sporadic and originates in the tumour. If not, it is possible that you might have Lynch syndrome and will be offered genetic testing.

If tumour test results show that there is a possibility that you might have Lynch syndrome, you will be offered genetic testing. Genetic testing will be able to confirm if you have Lynch syndrome.