Ask the expert: genetic testing for breast cancer
An article reproduced with permission from Associate Professor Judy Kirk and www.superliving.com.au. Sunday, 13 July 2008.
Q: I KNOW there are genetic tests for breast cancer but am not sure who should have them or how conclusive they are. And what happens if the results are positive?
Our expert, Associate Professor Judy Kirk is a cancer geneticist and director of the Familial Cancer Service at Sydney's Westmead Hospital. This service provides genetic counselling and testing for families with a strong history of cancer.
A: Firstly, it's important to understand that breast cancer is a common type of cancer. Therefore, it is not uncommon to have a family history of breast cancer. It is only some people who are at higher-than-average risk due to an inherited gene mutation in the family.
It's also important to be aware that only about 5% of all breast cancers are caused by the inherited gene mutations for which testing is currently available.
A 'strong family history' is one in which breast and/or ovarian cancer occur over several generations, often with young women affected. Genetic predisposition is more common in Jewish families.
The gene mutations known to increase breast cancer risk can be passed on by both the mother and the father, so it's important to ask about family history on both sides.
Available testing
The genetic testing currently available usually involves taking a blood sample from an affected family member to search for a causative gene mutation. The genes tested are known as BRCA1 and BRCA2. This is a 'search' test. These tests can sometimes be inconclusive and, as yet, no test is proven to be 100% conclusive.
If a causative mutation is identified, other adult family members can then be tested for it. This will determine whether or not they are at high risk and is known as a 'predictive test'. This is a more conclusive test.
Test results
If the results of such a predictive test show that a woman has a mutation on BRCA1 or BRCA2, then she is proven to be at high risk of breast and/or ovarian cancer. Generally, the risk of breast cancer is 60% to 80%; of ovarian cancer 10% to 50%.
Men with a BRCA gene mutation are shown to be at a small increased risk of prostate cancer and sometimes breast cancer.
A person found not to have the family BRCA gene mutation is not at increased risk of breast cancer – that person is at average risk, and he or she cannot pass the gene fault on to his or her children.
Actions from a positive result
A person found to be at increased risk can take the opportunity of additional screening, so that if cancer does occur, it can be detected early. Early detection offers the greatest chance of recovery.
However, risk-reducing surgery is also an option. This may include a risk-reducing mastectomy and/or removal of the ovaries and fallopian tubes (generally for women who have finished, or decided against, child bearing).
Removal of the ovaries and fallopian tubes for a high risk woman who is pre-menopausal may halve her breast cancer risk.
To find out more
To find out if a risk assessment and/or genetic testing is appropriate for you, call the Cancer Council Helpline on 13 11 20 and ask about Family Cancer Clinics.
For more information about breast cancer, visit the rest of our website at www.nbocc.org.au.
