Genetic testing of genes responsible for Lynch syndrome and polyposis syndromes
An underlying hereditary tendency to develop colorectal cancer (also known as "bowel cancer") can be identified by genetic testing in some people with this type of cancer or with colorectal polyps.
How can genetics affect cancer risk?
Most cancers are due to the gradual accumulation of errors in the genetic code in cells as a person ages. This accumulation of genetic errors is a natural and universal phenomenon.
A small proportion of people with cancer also have an underlying genetic error inherited from a parent, which predisposes them to develop cancer. Approximately one in 20 people with colorectal cancer have an inherited error in a gene that predisposed them to develop that cancer. An inherited error in one of these genes is also a common cause of a person having multiple colorectal polyps.
A patient’s personal history of cancer and polyps (type, age at diagnosis) and family history of cancer and polyps (number of affected relatives) can help the doctor estimate the chance of the patient having an underlying inherited genetic error.
If a person has an inherited genetic error that can cause colorectal cancer, they are at higher risk of developing cancer. However, some people with an inherited genetic error never develop cancer. On the other hand, there are many people who do not have a genetic error in any of these genes and who develop cancer.
Why consider testing for genetic errors?
A doctor may recommend genetic testing for inherited genetic errors in some patients with colorectal cancer or polyps to assist in deciding what treatment and follow-up to recommend. The result of the test may also be relevant for unaffected relatives who may have inherited the genetic tendency to develop cancer; they can have special tests or treatment to reduce the risk of cancer.
How are the genes tested?
DNA is extracted from a blood sample and analysed to check for inherited errors in selected genes. Genes that we currently test are listed on the Sonic Genetics website and reviewed regularly.
There are three categories of genetic error that the laboratory can find in the genetic code.
- the error may be significant and known to cause cancer
- the error may be benign, that is, it does not appear to cause any medical problems
- the significance of the error may be unknown, that is, there is insufficient medical evidence to categorise the error with confidence.
Please note that our test examines genes that cause many types of cancer. The test may identify a genetic error that can cause cancer other than colorectal cancer.
Testing for other hereditary cancers
The genes that can cause hereditary colorectal cancer can also cause other types of cancer. For this reason, a doctor may ask the laboratory to examine multiple genes in a person who has cancer that does not involve the colon or rectum.
The pros and cons of testing, the costs that may be involved, the availability of therapies and the potential for being involved in clinical trials of new drugs would be discussed by your doctor.
Genetic testing is used to determine the underlying genetic cause of your condition. The outcome of a genetic test may have consequences for both the person tested and for their relatives. It is important that all aspects are discussed and considered before testing.
Genetic counselling facilitates these discussions, giving you the opportunity to ask questions and to understand the implications of this test for you and your relatives.
It is accepted international practice that these issues be addressed with an experienced healthcare professional, such as a genetic counsellor, before testing is performed.
Arranging a test
- Your specialist will have completed a Hereditary cancer testing request form. Your specialist will discuss with you the purpose, scope and limitations of this test before you consent to having the investigation, and may also recommend that you discuss these matters with a genetic counsellor.
- Your blood sample can be taken at any of our pathology collection centres.
- If requested by your specialist, we will arrange for a genetic counsellor to contact you to discuss testing. For more details click here.
- Your result is reported back to your doctor, usually within four weeks of the laboratory receiving your blood sample.
These tests have Medicare rebates which, subject to the requirements of a Medicare descriptor being met, may cover all or part of the cost.
Medicare-rebated testing is available when requested by a medical specialist, such as a medical oncologist, surgeon or clinical geneticist.
If you have further questions, we recommend that you discuss your personal situation with your doctor.
The information on this website is provided for your general information and is not a substitute for the specific advice of your treating doctor.