Lynch syndrome is an inherited genetic condition that significantly raises your lifetime risk of developing several types of cancer, most notably colorectal and endometrial cancer. Roughly 1 in 279 people carry a Lynch syndrome mutation, though many don’t know it until a cancer diagnosis or family screening reveals it. The condition doesn’t cause cancer directly, but it disables one of your body’s key DNA repair systems, allowing errors to accumulate in cells over time.
How Lynch Syndrome Increases Cancer Risk
Your cells constantly copy their DNA, and small errors happen during every round of copying. Normally, a built-in proofreading system called mismatch repair catches and fixes those errors before they cause problems. Lynch syndrome is caused by an inherited mutation in one of four genes responsible for this repair system: MLH1, MSH2, MSH6, or PMS2. When one of these genes isn’t working properly, copying errors go uncorrected and pile up over time.
Repetitive stretches of DNA are especially vulnerable to these uncorrected errors, a phenomenon known as microsatellite instability. This instability is essentially the fingerprint of Lynch syndrome at the cellular level. As mutations accumulate in genes that control cell growth, the risk of a cell turning cancerous rises substantially. Mutations in MLH1 and MSH2 tend to produce the highest levels of instability and carry the greatest cancer risks, while MSH6 and PMS2 mutations generally lead to lower instability and somewhat lower, though still elevated, risk.
Which Cancers Are Linked to Lynch Syndrome
Colorectal cancer is the most well-known risk. For someone with a Lynch syndrome mutation, the lifetime risk of colorectal cancer ranges from 22% to 74%, compared to about 4% to 5% in the general population. The wide range depends largely on which gene is affected.
For women, endometrial cancer is equally concerning. The lifetime risk of uterine cancer for women with Lynch syndrome is 40% to 60%, and for those with MSH6 mutations specifically, it climbs to roughly 71% by age 70. The average age at diagnosis is 47 to 49, younger than in the general population. In many women with Lynch syndrome, endometrial cancer equals or exceeds their colorectal cancer risk.
Beyond the colon and uterus, Lynch syndrome raises risk for cancers of the:
- Ovaries: lifetime risk up to 11% to 17% depending on the gene involved
- Stomach: risk ranges from about 8% to 16%
- Urinary tract: including the kidneys, ureters, and bladder
- Small bowel, pancreas, biliary tract, and brain (typically glioblastoma)
- Skin: specific types of sebaceous gland tumors
Prostate cancer also appears on the list, though the degree of added risk is less clearly defined than for colorectal or endometrial cancers.
How Lynch Syndrome Is Identified
Many people first learn they have Lynch syndrome after being diagnosed with cancer, when tumor testing reveals signs of a mismatch repair defect. Two common tests are used on tumor tissue. Immunohistochemistry (IHC) stains the tumor to check whether the four repair proteins are present. If one or more is missing, it points to a specific gene problem. Microsatellite instability (MSI) testing checks the tumor DNA directly for the pattern of accumulated errors. IHC catches about 77% to 83% of cases, while MSI testing detects roughly 89% of MLH1/MSH2-related cases and 77% of MSH6-related ones.
If either test is abnormal, genetic testing through a blood or saliva sample confirms whether you carry an inherited mutation. Many cancer centers now perform IHC or MSI testing automatically on all colorectal and endometrial tumors, which has helped identify carriers who might otherwise have been missed.
Family history can also raise suspicion. Clinicians look for patterns like three or more relatives with Lynch-associated cancers across at least two generations, with at least one case diagnosed before age 50. But not every family with Lynch syndrome fits this pattern neatly, so tumor-based screening has become the more reliable entry point.
Screening and Surveillance
Once you know you carry a Lynch syndrome mutation, the goal shifts to catching any cancer early, when it’s most treatable. Current guidelines recommend starting colonoscopies between ages 20 and 25, or two to five years before the youngest cancer diagnosis in your family if that occurred before age 25. After the first colonoscopy, you’ll repeat it every one to two years for the rest of your life. This is far more frequent than the every-ten-years schedule recommended for average-risk adults, but the accelerated timeline reflects how quickly Lynch-related colorectal cancers can develop.
For stomach and small bowel cancers, upper endoscopy every three to five years starting between ages 30 and 35 is worth considering, particularly if you have a family history of gastric cancer or are of Asian ancestry. Urine testing to check for microscopic blood can help screen for urinary tract cancers in those with a relevant family history. Pancreatic cancer screening with endoscopic ultrasound or MRI may be recommended if pancreatic cancer runs in the family.
Risk-Reducing Surgery for Women
Given the high endometrial and ovarian cancer risk, preventive removal of the uterus and ovaries is a serious consideration for women with Lynch syndrome. In studies of women with confirmed mutations, more than half ultimately chose prophylactic hysterectomy, with a median age at surgery of about 42. The steepest jump in endometrial cancer incidence occurs between ages 50 and 60, so surgery before that window offers the greatest protective benefit.
This is a deeply personal decision that depends on your specific gene mutation, family history, whether you’ve completed childbearing, and your comfort with ongoing surveillance as an alternative. Women who opt against surgery typically undergo regular gynecological monitoring, though surveillance for endometrial cancer is less standardized and less proven than colonoscopy is for colorectal cancer.
Why Lynch Syndrome Cancers May Respond Well to Immunotherapy
There’s a meaningful silver lining to the biology of Lynch syndrome. Because these cancers accumulate so many mutations, they tend to produce a large number of abnormal proteins on their cell surfaces. The immune system recognizes these abnormal proteins as foreign, which is why Lynch-related tumors are often packed with immune cells. About 56% of these tumors show very high levels of immune cell infiltration, compared to 26% of cancers without mismatch repair problems.
This makes Lynch syndrome cancers particularly good candidates for immunotherapy, specifically checkpoint inhibitors that release the brakes on the immune system. Tumors with higher immune cell infiltration tend to respond better to these treatments. For people with advanced Lynch-related colorectal cancer, immunotherapy has become a front-line option, a shift that represents one of the most significant treatment advances in recent years for this population.
Inheritance and Family Planning
Lynch syndrome follows an autosomal dominant inheritance pattern, meaning you only need one copy of the mutated gene (from one parent) for your cancer risk to increase. If one of your parents carries the mutation, you have a 50% chance of inheriting it. Each of your children would face the same odds. This is why a single diagnosis in a family often triggers a cascade of genetic testing among relatives, and why identifying the condition in one person can be genuinely lifesaving for their siblings, children, and extended family members who can then begin early surveillance.