Tests and diagnosis

By Mayo Clinic Staff

If it's suspected that you have Lynch syndrome, your doctor may ask you questions about your family history of colon cancer and other cancers. This may lead to other tests and procedures to diagnose Lynch syndrome.

Family history

A family history of colon cancer and other cancers, particularly when they occur at a younger age, may alert your doctor to the possibility that you or members of your family may have Lynch syndrome.

Your doctor may refer you for further Lynch syndrome evaluation if you have:

  • Multiple relatives with any Lynch-associated tumors, including colorectal cancer. Examples of other Lynch-associated tumors include those affecting the endometrium, ovaries, stomach, small intestine, kidney, brain or liver.
  • Family members diagnosed with cancer at ages that are younger than the average for their type of cancer.
  • More than one generation of family affected by a type of cancer.

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 and sometimes from other tumors 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 that provided care may be able to supply a tissue sample. These tissue samples are often stored for many years.

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 gene 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 in the tumor.

Positive IHC or MSI test results indicate that you have malfunctions in the genes that are connected to Lynch syndrome. But results can't tell you whether you have Lynch syndrome because some people develop these gene mutations only in their cancer cells.

People with Lynch syndrome have these gene mutations in all of their cells. Genetic testing can determine whether you have these mutations.

Increasingly, IHC or MSI testing is being offered to anyone diagnosed with colon cancer to look for signs that may indicate Lynch syndrome. Doctors hope this will help identify families with Lynch syndrome that don't meet the usual criteria for genetic testing.

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.

Results of genetic testing may show:

  • A positive genetic test. A positive result, meaning that a gene mutation was discovered, doesn't mean that you're certain to get cancer. But it does mean your lifetime risk of developing colon cancer is increased.

    How much your risk is increased depends on which gene is mutated in your family and whether you undergo cancer screening to reduce your risk of cancer. Your genetic counselor can explain your individual risk to you based on your results.

  • A negative genetic test. A negative result, meaning a gene mutation wasn't found, is more complicated. If other members of your family have Lynch syndrome with a known genetic mutation, but you didn't have the mutation, your risk of 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 be misleading, since not everyone with Lynch syndrome has a genetic mutation that can be detected with current tests. You could still have a high risk of colon cancer — especially if you have a strong family history of colon cancer or your tumor testing revealed a high likelihood of Lynch syndrome.

  • A gene variation of unknown significance. Genetic tests don't always give you a yes or no answer about your cancer risk. Sometimes your genetic testing reveals a gene variation with an unknown significance. Your genetic counselor can explain the implications of this result to you.

Sometimes genetic testing for Lynch syndrome is done as part of a test for multiple cancer-related genetic mutations. Your genetic counselor can discuss the benefits and risks of genetic testing with you. He or she can explain what genetic testing can tell you and what it can't.

March 13, 2015