Targeted screening for Lynch syndrome in people with colorectal cancer and their relatives

What is Lynch syndrome?

Lynch syndrome is an inherited condition that increases the risk of developing certain types of cancer, especially colon cancer and endometrial cancer. It can also increase the risk of cancer in the ovaries, pancreas, stomach, small intestine, urinary tract, and the brain. These cancers often happen at a younger age compared to cancers that develop in people without Lynch syndrome.

What causes Lynch syndrome?

When the cells in our body divide to create new cells, our genetic code (DNA) is copied so that each new cell has its own copy. Sometimes mistakes can happen during this process. We have genes, called mismatch repair genes (MMR), that can find and fix these copying errors. If these genes don’t work properly then they can’t make the proteins which look for, and repair, mistakes in our DNA. Over time, these copy errors can build up and turn into cancer.

Lynch syndrome is where someone has a problem with one of four MMR genes (called MLH1, MSH2, MSH6, and PMS2). We all have two copies of every gene. Someone with Lynch syndrome will have one working and one non-working copy of one of the MMR genes. Their working gene copy can fix DNA errors. But if it gets damaged, then it can no longer repair the DNA in that cell, which can lead to cancer.

Lynch syndrome screening

If a person has Lynch syndrome, there is a 50% chance that every child they have will also have Lynch syndrome. UK estimates suggest that 1 in 500 people have Lynch syndrome. Most people will not know that they have Lynch syndrome, unless they (or a close relative) develop cancer and have genetic testing. When someone is diagnosed with Lynch syndrome, their close relatives (children, parents, brothers and sisters) can be tested to see if they also have the non-working gene. This is called cascade testing. People diagnosed with Lynch syndrome can be monitored for signs of cancer developing. They can also choose to make lifestyle choices to reduce their cancer risk.

Why are we doing an evidence map of Lynch syndrome screening in people with colorectal cancer and their relatives?

An evidence map is the first step in the review process for the UK National Screening Committee (UK NSC). It details what research (and what kind of research) has been done on a subject. It can help to highlight where there might be gaps in knowledge.

This evidence map will look at:

• Whether there are national or international guidelines about screening people with colorectal cancer and their relatives for Lynch syndrome.
• The evidence on tests that are used to identify Lynch syndrome in the relatives of people who have both Lynch syndrome and colorectal cancer.
• The evidence on how many people with Lynch syndrome (but do not have cancer) go on to develop colorectal cancer.

The UK NSC will use the results of this evidence map to decide whether a full or more detailed review should be done.