Types of Genetic Testing
Hereditary Germline Testing
Single Gene Sequencing
This type of genetic test detects changes in a particular gene. A mutation is an alteration in a gene that is disease-causing for inherited cancer risk. Some changes in genes do not affect the gene’s function and so are not disease-causing. A common example of this type of testing is sequencing of the BRCA1 and BRCA2 genes. If a mutation is found in one or both of these genes, the person's risk of developing breast and ovarian cancers is significantly increased.
Site-specific Mutation Testing
This type of genetic test is used for people who come from families in which one member has already tested positive for a mutation in a certain gene. Because the cancer-causing mutation has already been identified, the test looks for the one specific mutation in an individual from that family. The test results usually are more clear and uninterpretable. The result will either be positive (the mutation has been detected and therefore was inherited) or negative (the mutation has not been detected and therefore was not inherited).
Cancer gene panels use next generation sequencing technology to evaluate multiple genes at the same time for genetic alterations which may contribute to inherited risk for cancers in families. Gene panels can vary in size from just two genes (i.e., BRCA1 and BRCA2) to larger panels that include more than 50 genes. Cancer gene panels are less expensive and more efficient than single gene sequencing. However, cancer gene panels provide more complex results such as uncertainty of clinical significance or mutations in genes for which clear risk reduction strategies are not established.
Tumor Molecular Testing
Tumor molecular testing approaches are used to identify tumor markers that may be used to help diagnose cancer, predict a patient's response to certain cancer therapies, check a patient’s response to treatment or determine whether cancer has returned.
Two types of tumor testings that are commonly used for people who are suspected of having Lynch syndrome - and are more likely to have colon cancer and other cancers - are Immunohistochemistry (IHC) and Microsatellite Instability (MSI). These tests can reveal whether a cancer was caused by the genes related to Lynch syndrome.
Tumor tissue is exposed to special stains that will color the tissue only if a specific protein is present. If the specific protein is missing the stain will not color the tissue. To test for Lynch syndrome, four specific stains are used to detect the MLH1, MSH2, MSH6 and PMS2 proteins. If one or more of these proteins is missing, there may be an increased risk for Lynch syndrome.
MSI testing looks at certain regions of the DNA called microsatellites to see whether there is evidence suggesting lack of DNA mismatch repair as seen in Lynch syndrome. Based on specific microsatellite patterns, people with MSI-high tumors have a higher risk of having Lynch syndrome.
Tumor Genomic Testing
Next generation sequencing technologies have led to the development of many tumor-based tests that doctors can order in specific clinical settings to assist with decisions for treatment and cancer management. These tests are also called “somatic” gene tests as they are assessing genetic and/or genomic changes in genes within specific tissues.
For more information about genetic testing, please call Sue Miller-Samuel, RN, MSN, Advanced Practice Nurse in Genetics, at 215-955-9098 or Stephanie Winheld, MS, Genetic Counselor, at 215-955-1011.