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Tests and diagnosis
By Mayo Clinic staffIf your doctor suspects you may have Lynch syndrome, he or she may ask you questions about your family history of colon cancer. This may lead to other tests and procedures to diagnose Lynch syndrome.
Family history
A family history of colon cancer, particularly when it occurs at a younger age, may alert your doctor to the possibility that you or members of your family may have Lynch syndrome. Researchers have devised guidelines, called the Amsterdam criteria, to determine who should be referred for further Lynch syndrome testing.
The Amsterdam criteria include:
- Three relatives with any HNPCC-associated tumor, including colorectal cancer. Other HNPCC-related tumors are those affecting the endometrium, ovaries, stomach, small bowel, kidney, brain, and skin, among others. At least two of these family members should be first-degree relatives, such as a parent, child or sibling.
- Two successive generations of affected family members.
- Diagnosis of one family member with this cancer before age 50.
While the Amsterdam criteria give doctors a general idea of which families may pass the genetic mutations associated with Lynch syndrome, the criteria aren't perfect. Many people meet the Amsterdam criteria, but aren't found to have Lynch syndrome. Conversely, many people with Lynch syndrome have families that don't meet the Amsterdam criteria.
If your family history meets the Amsterdam criteria, your doctor may recommend you undergo further testing.
Tumor testing
If you or someone in your family has been diagnosed with cancer, special testing may reveal whether the tumor has specific characteristics of Lynch syndrome cancers. Samples of cells from a colon cancer, a precancerous colon polyp or an endometrial cancer can be used for tumor testing. If you or someone in your family has been diagnosed with cancer in the last several years, the hospital where you received care may be able to supply a tissue sample. These tissue samples are often stored for 10 years or longer.
Tumor testing can reveal whether your cancer was caused by the genes related to Lynch syndrome. Tumor tests include:
- Immunohistochemistry (IHC) testing. IHC testing uses special dyes to stain tissue samples. The presence or absence of staining indicates whether certain proteins are present in the tissue. Missing proteins may tell doctors which mutated genes caused the cancer.
- Microsatellite instability (MSI) testing. Microsatellites are sequences of cellular DNA. In people with Lynch syndrome, there may be errors or "instability" in these sequences.
Positive IHC or MSI test results indicate that you have mutations in the genes that are connected to Lynch syndrome. But results can't tell you if you have Lynch syndrome or not because it's possible to spontaneously develop these gene mutations. About 15 percent of all colon cancers have a positive MSI result, but most aren't caused by Lynch syndrome.
Genetic testing
Genetic testing looks for changes in your genes that indicate that you have Lynch syndrome. You may be asked to give a sample of your blood for genetic testing. Using special laboratory analysis, doctors look at the specific genes that can have mutations that cause Lynch syndrome.
A positive genetic test result, meaning that gene mutations were discovered, doesn't mean that you're certain to get cancer. But it does mean your lifetime risk of developing colon cancer is thought to be about 60 percent to 80 percent. That means that for every 100 people with Lynch syndrome, between 60 and 80 people will develop colon cancer, while some 20 to 40 people won't develop colon cancer. Your risk of other cancers also is increased.
A negative result, meaning gene mutations weren't found, is more complicated. If other members of your family have been found to have Lynch syndrome, but you didn't have the genetic mutations, your risk of colon cancer is the same as the general population. If you're the first in your family to be tested for Lynch syndrome, a negative result may still indicate that you have a high risk of colon cancer — especially if you have a strong family history of colon cancer.
Your genetic counselor can discuss the benefits and risks of genetic testing with you. He or she will explain what genetic testing can tell you and what it can't.
