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A negative genetic test results means that no mutation was found in any of the genes associated with cancer risk that were included in the test panel. Although good news, a negative genetic test may not provide clear information cancer risk. A negative genetic test result can have several different meanings depending on the individual and family circumstances of the person tested.
In a family where a genetic mutation has already been identified, a negative test may be considered a "true negative." This means that the person does not have a higher risk for cancer than the general population. In a family with a known mutation, screening recommendations are different for someone who tests negative for the known mutation than for someone who tests positive. However, since cancer is a common disease and since most cancer has no known cause, a negative genetic test does not guarantee that a person won’t develop cancer in his or her lifetime.
In some families with multiple cases of cancer, genetic testing doesn't reveal any answers. In a family with many cases of cancer where all members test negative for a mutation; these results are called "uninformative negative." The term "uninformative" means that experts cannot find the cause of the familial cancer. One possibility is that there is an undiscovered genetic mutation in the family. Other possibilities include a shared behavior (such as smoking) or a shared environmental exposure. As genetic testing technology improves, it is possible that future genetic testing could reveal a cause for the cancer in a family that had uninformative testing in the past. Families with uninformative negative results are encouraged to contact a genetics expert periodically to update their medical history and learn if there are any new genetic tests that may provide additional clues.
In the past, some tests failed to identify certain BRCA1 and BRCA2 mutations known as 'rearrangements' as well as other mutations. Some families that previously tested as "uninformative negative" for BRCA in the past may actually harbor a BRCA mutation.
Additionally, newer gene mutations have been discovered that also increase the risk for inherited cancers. Mutations in these other genes will not show up in older tests, ordered before 2014 that looked only for mutations in BRCA1 and BRCA2. Several laboratories offer gene panel tests that search for mutations in many different genes associated with hereditary cancer risk. Members of families with uninformative negative results may still be at high-risk for cancer and may want to consider panel testing.
A specialist in cancer genetics is the best person to interpret genetic test results and help you determine whether additional genetic test may be appropriate for a your family.