Introduction: Who Should Consider Diagnostic Testing

If you have family members who developed colorectal cancer before age 50, or if several relatives across generations have had cancers of the colon, uterus, stomach, or ovaries, you might benefit from diagnostic testing for hereditary non-polyposis colorectal cancer syndrome. This condition runs in families and dramatically increases the risk of developing certain cancers during a person’s lifetime.^[1]

Anyone who personally develops colorectal cancer, especially before reaching age 50, should discuss with their healthcare provider whether testing for this syndrome might be appropriate. Women diagnosed with endometrial cancer, particularly at younger ages, should also consider evaluation. The syndrome affects men and women equally, though women face additional risks due to cancers of the reproductive system.^[2]

If someone in your immediate family has already been diagnosed with Lynch syndrome—the genetic condition underlying hereditary non-polyposis colorectal cancer—you should talk to your doctor about getting tested yourself. Children of someone with Lynch syndrome have a 50 percent chance of inheriting the altered gene, making early identification important for proper monitoring and prevention strategies.^[6]

Early identification of this syndrome matters because people who carry the genetic mutations have a much higher lifetime risk of cancer compared to the general population. Some estimates suggest that up to 80 percent of people with Lynch syndrome will develop colorectal cancer during their lifetime, and women face up to a 60 percent risk of endometrial cancer. Knowing your status allows you and your healthcare team to create a personalized screening and prevention plan.^[2]

Understanding the Disease and Its Genetic Basis

Hereditary non-polyposis colorectal cancer develops when you inherit mutations in genes that normally help repair mistakes during DNA replication—the process by which cells copy their genetic material before dividing. These genes, known as mismatch repair genes, include MLH1, MSH2, MSH6, PMS2, and EPCAM. When these genes work properly, they fix errors that naturally occur when DNA is copied. But when mutations disable them, errors accumulate over time, and cells are more likely to become cancerous.^[1]

Unlike some inherited cancer syndromes that cause hundreds or thousands of polyps to grow throughout the colon, hereditary non-polyposis colorectal cancer typically causes few or no extra polyps compared to what the general population experiences. However, the polyps that do form are more likely to develop into cancer, and they do so at younger ages. This explains why the condition is called “non-polyposis”—it’s a way of distinguishing it from other hereditary colon cancer syndromes that cause numerous polyps.^[15]

The syndrome is inherited in what geneticists call an autosomal dominant pattern. This means that inheriting just one copy of a mutated gene—from either your mother or father—is enough to increase your cancer risk substantially. If one of your parents has the mutation, you have a 50-50 chance of inheriting it. If you do inherit it, you also have a 50 percent chance of passing it to each of your children.^[4]

The specific gene that is mutated can affect your cancer risk profile. For instance, people with mutations in MLH1 or MSH2 genes tend to face higher cancer risks and earlier ages of onset compared to those with MSH6 or PMS2 mutations. Understanding which gene is affected can help your healthcare team tailor your surveillance and prevention strategies more precisely.^[9]

Classic Diagnostic Methods for Identifying the Syndrome

Physical Examination and Medical History

When you visit your healthcare provider with concerns about hereditary cancer risk, they will begin with a thorough medical history discussion. Your provider will ask detailed questions about any cancers you’ve personally had, your age when diagnosed, and the location and type of cancer. They’ll also want to know about your family medical history, including which relatives have had cancer, what types of cancer they developed, and how old they were at diagnosis.^[1]

Your provider will pay special attention to patterns that suggest hereditary non-polyposis colorectal cancer, such as multiple family members with colorectal or endometrial cancer across at least two generations, with at least one person diagnosed before age 50. These patterns help distinguish inherited cancer syndromes from cancers that occur by chance. If you’ve already been diagnosed with colorectal cancer, your provider will perform a physical examination and may conduct a colonoscopy—a procedure where a flexible tube with a camera examines the inside of your colon and rectum.^[1]

Amsterdam Criteria for Clinical Diagnosis

Healthcare providers use specific guidelines called the Amsterdam criteria to identify families that might have hereditary non-polyposis colorectal cancer. These criteria were developed to standardize who should be considered for further testing. According to these guidelines, a family meets criteria when they have at least three relatives with cancers associated with the syndrome, affecting at least two successive generations, with at least one cancer diagnosed before age 50. Additionally, one of the affected individuals must be a first-degree relative—meaning a parent, sibling, or child—of the other two.^[2]

However, these criteria were developed before genetic testing became widely available, and many families with the syndrome don’t meet all these strict requirements. That’s why healthcare providers now use more flexible screening approaches to identify people who might benefit from testing.^[7]

Tumor Tissue Testing

If you’ve been diagnosed with colorectal or endometrial cancer, one of the first diagnostic steps involves testing your tumor tissue itself. This testing looks for signs that the cancer might be related to hereditary non-polyposis colorectal cancer syndrome. Two main tests are performed on tumor samples.^[7]

The first is called immunohistochemistry, or IHC. This laboratory technique uses special stains to check whether the mismatch repair proteins are present in your tumor cells. When these proteins are absent or reduced, it suggests that the genes responsible for making them aren’t working properly. This is described as “mismatch repair deficiency” or “loss of mismatch repair protein expression.” Finding this pattern doesn’t definitively prove you have Lynch syndrome, but it’s an important clue that warrants further investigation.^[7]

The second test examines microsatellite instability, often abbreviated as MSI. Microsatellites are short, repetitive sequences of DNA scattered throughout your genetic material. When mismatch repair genes aren’t working, errors accumulate particularly in these repetitive regions, causing them to become unstable. A laboratory test called polymerase chain reaction, or PCR, can detect this instability. Tumors are classified as having high microsatellite instability (MSI-H) when many of these sequences show errors, which strongly suggests mismatch repair problems.^[7]

Both IHC and MSI testing are sensitive and usually produce results that agree with each other. Many medical organizations now recommend that all patients diagnosed with colorectal or endometrial cancer undergo these tumor tests, regardless of age or family history, as a universal screening approach to identify those who need genetic counseling and testing.^[7]

Genetic Testing for Inherited Mutations

The definitive way to diagnose hereditary non-polyposis colorectal cancer syndrome is through germline genetic testing. This type of testing examines the DNA from your normal cells—not cancer cells—to determine whether you were born with mutations in the mismatch repair genes. The test is typically performed using a blood sample, though sometimes a saliva sample can be used.^[1]

Before undergoing genetic testing, most people meet with a genetic counselor—a healthcare professional specially trained to help people understand their cancer risks, the benefits and limitations of genetic testing, and what the results might mean for themselves and their family members. The counselor will review your personal and family medical history in detail, explain how the syndrome is inherited, and discuss what actions might be recommended based on your test results.^[3]

The genetic test searches for mutations in the five genes most commonly associated with Lynch syndrome: MLH1, MSH2, MSH6, PMS2, and EPCAM. Testing has become increasingly sophisticated and can now identify not just large obvious mutations but also small changes that might affect how the genes function. The laboratory will issue a report indicating whether a mutation was found, and if so, which gene is affected.^[6]

Test results fall into three main categories. A “positive” or “pathogenic” result means that a disease-causing mutation was identified, confirming that you have Lynch syndrome. A “negative” result means no mutations were found in the tested genes, though this doesn’t completely eliminate all cancer risk—it just means your risk is similar to that of the general population. Sometimes results are “uncertain” or show a “variant of uncertain significance,” meaning a genetic change was found but scientists aren’t yet sure whether it causes disease. These uncertain results can be frustrating, but as research advances, many are eventually reclassified as either harmful or benign.^[7]

In situations where there is strong suspicion for hereditary non-polyposis colorectal cancer based on family history or early cancer diagnosis, your healthcare provider might recommend proceeding directly to germline genetic testing without first testing tumor tissue. This approach can be appropriate when tissue isn’t available for testing or when time is a concern.^[7]

Ruling Out Other Hereditary Syndromes

Part of the diagnostic process involves making sure that your cancer pattern isn’t better explained by a different hereditary cancer syndrome. The most important condition to distinguish from hereditary non-polyposis colorectal cancer is familial adenomatous polyposis, or FAP. Unlike hereditary non-polyposis colorectal cancer, FAP causes hundreds to thousands of polyps to carpet the lining of the colon, typically beginning in the teenage years or early twenties. People with FAP have nearly a 100 percent chance of developing colon cancer if their colon isn’t removed. FAP is caused by mutations in different genes—primarily the APC gene—than those involved in Lynch syndrome.^[1]

Your healthcare provider will review your colonoscopy findings and family history to determine whether the pattern fits hereditary non-polyposis colorectal cancer or another syndrome. If you have numerous polyps, genetic testing might focus on FAP-associated genes instead.^[15]

Diagnostics for Clinical Trial Qualification

If you’re considering participating in a clinical trial studying treatments or prevention strategies for hereditary non-polyposis colorectal cancer syndrome, you’ll need to undergo specific diagnostic tests to determine whether you’re eligible. Clinical trials have strict entry criteria to ensure that the participants enrolled are appropriate for the study being conducted and that results will be scientifically meaningful.^[2]

Most clinical trials for Lynch syndrome require confirmed genetic testing showing that you carry a pathogenic mutation in one of the mismatch repair genes. You’ll need to provide documentation from a certified laboratory showing your test results. Some trials may specify which genes qualify—for instance, a study might only enroll people with MLH1 or MSH2 mutations because these are associated with the highest cancer risks.^[7]

If you’ve been diagnosed with cancer, trials testing treatments will typically require tumor tissue testing to confirm that your cancer shows the characteristic features of Lynch syndrome-associated tumors, such as mismatch repair deficiency or high microsatellite instability. This helps ensure that the treatment being studied is appropriate for your specific tumor type.^[7]

Additional standard diagnostic tests often required for clinical trial enrollment include imaging studies to determine the extent of any cancer present. These might include colonoscopy to examine your colon, pelvic ultrasound or endometrial biopsy to evaluate your uterus if you’re a woman, or various scans such as CT or MRI to check for cancer spread. Blood tests measuring liver and kidney function, blood cell counts, and other health markers are typically required to ensure you’re healthy enough to safely participate in the trial.^[1]

For prevention trials—studies testing whether certain interventions can reduce cancer risk in people with Lynch syndrome who haven’t yet developed cancer—you’ll need baseline colonoscopy and potentially other screening tests to confirm that you don’t currently have cancer. These baseline tests also establish a starting point for monitoring whether the prevention strategy being studied is effective.^[7]

Surveillance and Monitoring After Diagnosis

Once you’ve been diagnosed with Lynch syndrome, regular surveillance becomes a crucial part of your healthcare. These aren’t one-time diagnostic tests but rather ongoing monitoring to detect cancer at the earliest possible stage, when treatment is most likely to be successful. Your healthcare team will create a personalized surveillance schedule based on which gene is mutated, your age, and your personal and family cancer history.^[9]

For colorectal cancer surveillance, most guidelines recommend that people with Lynch syndrome begin colonoscopy screening between ages 20 and 25, or two to five years younger than the earliest colorectal cancer diagnosis in your family, whichever comes first. Unlike the general population, who typically undergo colonoscopy every 10 years, people with Lynch syndrome should have colonoscopies every one to two years. These more frequent examinations allow doctors to find and remove polyps before they have time to develop into cancer.^[12]

Women with Lynch syndrome face elevated risks of endometrial and ovarian cancer, so additional surveillance is recommended. This typically includes annual endometrial sampling—a procedure where a small amount of tissue is removed from the uterine lining to check for abnormal cells—beginning between ages 30 and 35. Transvaginal ultrasound may also be performed to examine the ovaries and uterus. However, it’s important to understand that surveillance for gynecologic cancers is not as effective at detecting early disease as colonoscopy is for colorectal cancer. For this reason, many women with Lynch syndrome choose to have their uterus and ovaries removed after they’ve completed childbearing, which significantly reduces cancer risk.^[9]

Depending on your specific gene mutation and family history, your healthcare provider might recommend additional surveillance for other cancers associated with Lynch syndrome. This could include upper endoscopy—similar to colonoscopy but examining your esophagus, stomach, and small intestine—particularly if you have family members who developed gastric or small bowel cancer. Urine tests to check for blood might be recommended to screen for urinary tract cancers. Annual skin examinations by a dermatologist can help detect unusual skin tumors associated with some forms of Lynch syndrome.^[9]

Your healthcare provider will work with you to develop a comprehensive surveillance plan that balances the benefits of early cancer detection against the time commitment, costs, and potential discomfort of frequent testing. Following your surveillance schedule carefully provides the best opportunity to catch any cancers that do develop at the most treatable stage.^[12]

Family Testing and Cascade Screening

When you’re diagnosed with Lynch syndrome, an important step is informing your biological relatives that they might also carry the mutation. Since the syndrome is inherited, your parents, siblings, and children each have a 50 percent chance of having the same genetic change. Your extended family members—aunts, uncles, cousins, nieces, and nephews—may also be at risk, depending on which side of the family the mutation came from.^[6]

Once a mutation has been identified in one family member, testing other relatives becomes more straightforward and often less expensive. The laboratory can look specifically for that exact mutation rather than searching through all the genes. This targeted testing gives clear yes-or-no answers: either you inherited the family mutation or you didn’t. Relatives who test negative for the known family mutation can be reassured that their cancer risk is similar to that of the general population, while those who test positive can begin appropriate surveillance and risk-reduction strategies.^[7]

Genetic counselors can help you navigate the sometimes difficult conversations about sharing genetic information with family members. Some people find it challenging to discuss cancer risk with relatives, especially if relationships are strained or family members live far apart. Your genetic counselor can provide resources and even help facilitate family communication about testing when needed.^[3]