The BRCA1 and BRCA2 genes are responsible for suppressing tumours. If you have a mutation in either of these genes, you are at a higher risk of developing breast cancer.
In 2013, the news of Angelina Jolie’s preventative double mastectomy shocked the world. Her decision seemed like a radical response to the risk of developing breast cancer. But as it turns out, for many people with an increased genetic risk of breast cancer, doctors recommend this preventative surgery. So, how do you know if you have a genetic risk of breast cancer?
We chatted to Shelley Macaulay, the genetic counselling manager at the Division of Human Genetics of the National Health Laboratory Service, about how genetic testing works and who should get tested. Here is what she had to say:
There are two BRCA (literally “breast cancer”) genes that every person has within their DNA: BRCA1 and BRCA2. When these genes are functioning normally they act as tumour suppressor genes. Their role is to prevent tumours from forming. However, if you have a mutation, which is a fault, in one of the genes, the gene loses its tumour suppressor function and you are predisposed to developing cancer.
Mutations in either of the BRCA genes results in a genetic condition called Hereditary Breast and Ovarian Cancer Syndrome (HBOCS). If an individual has HBOCS they are at increased risk of developing breast cancer (up to 87% risk) and ovarian cancer (up to 63% risk). There are also other cancers that are associated with the condition (prostate cancer, stomach cancer, pancreatic cancer).
Both men and women can carry mutations in their BRCA genes, and people who carry a BRCA mutation have a 50% chance of passing it on to their children.
If you are concerned about your risk of carrying a BRCA mutation, you should see a genetic counsellor. Genetic counsellors are professionals qualified at the Masters Degree level who are trained to assess how likely it is that a genetic cancer syndrome will be present in an individual or family.
Genetic testing is only justified in people who are considered to be at moderate to high-risk of having an inherited cancer syndrome. We look at your family medical history to determine risk. Some of the following characteristics are usually present in moderate to high-risk cancer families:
- At least three first-degree relatives (a parent, sibling or child) affected with HBOCS-associated cancers.
- The cancers develop at a younger age than the average age at which that cancer usually develops (under 50 years for breast cancer and under 60 years for ovarian cancer).
- An individual in the family has multiple primary tumours. This means that they have both breast and ovarian cancer, or have breast cancer in both breasts.
- A male in the family has been diagnosed with breast cancer.
- Individuals belong to higher risk ethnic groups (such as Ashkenazi Jewish ancestry or Afrikaner ancestry).
Lastly, if individuals have a family member who has tested positive for a BRCA mutation they should see a genetic counsellor to discuss their risk of also carrying the mutation.
Only about 5% to 10% of breast cancers are genetic.
The majority of breast cancers are sporadic, which means that they occur in patients with no genetic history of cancer. Only about 5% to 10% of breast cancers are genetic. Therefore, testing every woman for BRCA mutations would be unnecessary and very expensive.
Also, women who test negative for a BRCA mutation still have the normal risk of any other woman in the population of developing breast cancer – which is around 12% - so they still have to carry out regular breast examinations.
It is always best to start testing on the affected family member – the person who has had cancer. This is because if we know what mutation they have, we can do tests for that specific mutation among their family members. Also, in population groups that have a higher likelihood of BRCA mutations, we know which specific mutations to test for first.
Genetic testing is like driving along a highway: you start at the beginning and drive along until you hit a pothole – which is the mutation. But if you have a way of knowing exactly where the pothole is before you start, then you don’t have to do all that driving.
BRCA mutation screening is carried out with a simple blood test. The costs for BRCA testing can range from R1 500 if we are searching for a known mutation, to R10 000 if full gene sequencing needs to be carried out. Genetic testing is generally paid for by the state for patients seen through government hospitals. The results, if we are testing for a known mutation, are usually available within a couple of weeks, whereas a full genetic sequence can take anywhere from four to twelve weeks.
If a woman tests positive for a BRCA mutation, she is at significantly increased risk of developing breast and ovarian cancer. If you test positive, you have two options: increased screening or prophylactic (preventative) surgery.
Breast cancer screening would involve monthly self-breast examinations, annual clinical breast examinations (by a doctor) and annual mammograms or breast MRIs (radiologists will decide which is best based on a woman’s age and density of breasts).
Prophylactic surgery for breast cancer would involve a double mastectomy which reduces your risk of developing breast cancer by at least 90%.
In terms of ovarian cancer, unfortunately, screening measures are very poor because ovarian cancer is difficult to detect early – even with annual gynaecological examinations. For women with a BRCA mutation, prophylactic surgery to remove the ovaries and fallopian tubes is recommended after childbearing.
If your family history of cancer suggests that you may have an inherited cancer syndrome, but you have no living relatives with cancer, you may still be offered genetic testing. However, there are limitations to interpreting your results. For example, if you had a family member who died from breast or ovarian cancer, you could test negative for a BRCA mutation, but there might be a different genetic cancer syndrome involved that might put you at greater risk of getting cancer.
Both men and women can carry BRCA mutations and this has implications for their personal risks of certain cancers as well as the risks to their children. If a man’s personal or family history is suggestive of an inherited cancer syndrome, he should seek genetic counselling and possible testing.
If you would like to find out more information about inherited breast cancer, the risks and the available testing, contact the Clinical and Counselling Section of the Division of Human Genetics at the National Health Laboratory Service on 011 489 9223 or email human.genetics@nhls.ac.za.