The benefit of genetic analysis to a patient is primarily based on their family history. Family history also allows us to estimate the risk of breast cancer in other relatives. This can be especially important whenever genetic analysis fails to reveal a mutation.
If there is a suspicion of a hereditary form of breast cancer, two tests can be performed:
This is a molecular analysis to identify a mutation in the BRCA1 or BRCA2 gene. A DNA test is primarily offered to patients who have breast or ovarian cancer and any other affected family members. The rationale behind this is that it is still possible for a female relative who is not a carrier of the mutation to develop breast or ovarian cancer. This person has non-hereditary disease, known as a phenocopy. If the DNA test is only performed on this woman, a false negative result would apply to the whole family. Therefore to minimize this risk, all affected relatives are tested.
Despite recent technological advances, a DNA test takes approximately six months. The analysis is provided by the health care systems of several European Countries.
Predictive or screening test
If the DNA test in an affected patient is positive, it is possible to search for the mutation in all unaffected relatives, who give their consent. This is called a predictive or screening test and as it is targeted, it takes less time.
Based on this screening investigation, we can evaluate an individuals’ risk of developing breast or ovarian cancer: women who have not inherited the mutation have the same risk as the general population, whilst women who carry the mutation have a markedly increased risk.
This information is also of benefit to male relatives, because their risk of colon and prostate cancer may be increased. They can also pass on the mutation to their children, which is of particular importance if they have daughters.
When the DNA test fails to detect the mutation in an affected woman, unfortunately we cannot exclude hereditary breast cancer. The test may be falsely negative, or a mutation in another, as yet unidentified gene, may be present. The genetic consultation for non-affected relatives is based on the family history, as screening is not possible.
In a family in which all the women who developed breast or ovarian cancer have died, a predictive test can still be offered to unaffected first-degree relatives. The probability that these women are carriers is 50%, so it is still possible that although a BRCA1 or BRCA2 mutation was present, that person did not inherit it and the result may be falsely negative. If however a mutation is found, we can confirm that the family does indeed carry the mutation.
An important step before undertaking a genetic analysis is obtaining the patient’s consent. A number of items should be discussed, so that the patient is fully informed of the process, the possible result and future implications (Table).
Table Discussion points prior to obtaining informed consent for a genetic test:
- the option of not being tested
- the purpose, reliability and method of testing
- the cost
- the implications of a positive or negative result
- the possibility of gaining no useful information
- the disadvantages of genetic research
- the confidentiality of the results
- the risk of future discrimination
- the risk of children carrying the mutation
In additon to providing genetic information, increasing attention is being applied to the psychological support offered to patients and their families, in both the screening and diagnostic setting. This support focuses on enabling a patient to:
- process and deal with a positive test result,
- communicate with her family,
- address concerns about her children or relatives being potential carriers,
- choose a preventitive strategy,
- limit the impact of the test on her relationship or desire to have children.