How a negative test result will be interpreted depends on whether or not someone in the tested person’s family is known to carry a harmful BRCA1 or BRCA2 mutation. If someone in the family has a known mutation, testing other family members for the same mutation can provide information about their cancer risk. If a person tests negative for a known mutation in his or her family, it is unlikely that they have an inherited susceptibility to cancer associated with BRCA1 or BRCA2. Such a test result is called a “true negative.” Having a true negative test result does not mean that a person will not develop cancer; it means that the person’s risk of cancer is probably the same as that of people in the general population.
In cases in which a family has a history of breast and/or ovarian cancer and no known mutation in BRCA1 or BRCA2 has been previously identified, a negative test result is not informative. It is not possible to tell whether an individual has a harmful BRCA1 or BRCA2 mutation that was not detected by testing (a “false negative”) or whether the result is a true negative. In addition, it is possible for people to have a mutation in a gene other than BRCA1 or BRCA2 that increases their cancer risk but is not detectable by the test(s) used.