Predictive/Pre-symptomatic genetic testing
This is defined as a test on an unaffected family member for a gene already known to be present in their biological family. Most predictive genetic tests are available for individuals with a 25%-50% chance of inheriting the gene fault that exists within that family.
It should not be done if a gene variant is not known to definitely cause a cancer predisposition risk, as it would not change clinical advice. It could actually be damaging to test because it might falsely reassure individuals.
It is a personal decision to have the test and no one can insist you do have testing. Any decision to test should be made after having genetic counselling (see section on genetic counselling).
There are advantages and disadvantages to testing
- Knowing your gene status (if you carry the gene or not) means you can use risk management strategies to either reduce your risk or ensure early diagnosis.
- It will reduce anxiety – if uncertainty makes you more anxious.
- A positive result may cause anxiety that is difficult to control and lead to psychological issues.
- It can increase worry about risks of passing the gene fault on to offspring. Genetic testing for adult onset conditions is not offered to individuals less than 18 years.
It is possible to test a person who is unaffected by a relevant cancer but does have a concerning family history if they feel the advantages outweigh the disadvantages for them.
Testing involves molecular analysis of DNA (usually from a blood sample but it is possible to use saliva or buccal (cheek swab) samples) to see if any gene faults can be identified. There are considerations to think about in doing this and we can talk through these.
If a gene fault is not found it does not necessarily rule out one is not actually there due to technological constraints and your family history. This means that surveillance advice is still needed and even risk reducing surgery, in certain situations. This can be discussed with the genetic counsellors and specialists with advice given.