Lynch Syndrome Explained: DNA Repair and Cancer Risk

This page is for people who have heard of Lynch syndrome in their family or at a clinic. It explains what the condition is, how it is found, and why it changes screening.

Lynch syndrome is a condition passed down in families. It is caused by changes in genes whose job is to help cells repair DNA. If those genes are faulty, small DNA errors can build up, and certain cancers become more likely.

The condition is present from birth. It can be passed from a parent to a child. That is why it can show up across several relatives.

Lynch syndrome raises cancer risk. But knowing about it opens the door to screening that can catch cancer early, or even prevent it.

Lynch syndrome is not something a person catches. It is not something habits bring on later. It is an inherited change, carried in every cell of the body from the start of life. Because it is inherited, each close blood relative may or may not carry the same change.

That sets it apart from cancers that seem to run in families for other reasons, such as shared habits or chance.

Every time a cell copies its DNA, small mistakes can happen. Cells have repair systems that fix these errors. Lynch syndrome involves inherited changes in the genes that run this repair work.

When repair is less reliable, errors pile up faster. In time, one cell may start to grow out of control. The change raises risk, but it does not guarantee cancer.

Lynch syndrome most raises the risk of:

• Colorectal cancer — cancer of the colon or rectum
• Endometrial (uterine) cancer — cancer of the lining of the uterus

It can also raise the risk of some other cancers, such as ovarian and stomach cancer. One key feature is that these cancers often appear at younger ages than they would in the general population.

Because the change is inherited, it can travel from one generation to the next. One useful clue is a family pattern of colon and endometrial cancer, above all at young ages. Another is one relative having more than one related cancer.

When possible, testing often begins with a relative who has had cancer. Their result tends to be the most useful starting point for everyone else.

A genetic test, usually done on blood or saliva, confirms Lynch syndrome. Before that, a genetic counselor or doctor looks at personal and family history. Sometimes the path starts with the tumor instead. A person's cancer is tested for features that point to Lynch syndrome, and testing for inherited risk follows.

The biggest benefit of knowing about Lynch syndrome is that it changes the screening plan. People with Lynch syndrome usually start colorectal screening younger and repeat it more often than adults at average risk.

A colonoscopy (a look inside the colon with a thin, lighted tube) is especially valuable. It can find and remove polyps, small growths, before they turn into cancer. In this way screening can help prevent cancer, not just find it. Checks for other related cancers may also be advised, based on which gene is involved and the person's own history.

A Lynch syndrome diagnosis matters for blood relatives too. A brother, sister, parent, or child might carry the same change. They could benefit from testing and a screening plan built for them. A genetic counselor can help a person understand their result, plan their own screening, and think through how to share the news with family.

Learning that Lynch syndrome may be in your family can feel unsettling. But it is best seen as useful information, not a verdict. Some people with the condition never develop cancer at all.

The practical value is in what it unlocks. You get a screening plan built for you, one that can catch cancer early or prevent it. And relatives get a chance to learn about their own risk. A doctor or genetic counselor can review your family history, explain whether testing makes sense, and turn what you learn into a clear, personal plan.