Hereditary Breast and Ovarian cancer syndrome and the BRCA1 or BRCA2 genes
The BRCA1 and BRCA2 genes were the first genes identified as causing a very high risk of breast and ovarian cancer.
BRCA1 and BRCA2 are important for fixing the mistakes that occur in the DNA of cells. Specifically, they fix double strand breaks. The pathway is known as homologous repair. You can think of them as spell-checker genes. Scientists call them tumour suppressor genes.
The woman, Dr Mary-Claire King, who found the first gene, called it the B-R-C-A-1 gene. It stands for BReast CAncer One. But, just like most people name Christopher are called Chris, most people say BraCar. (Although, if you are ever around Dr King or are presenting at a genetics conference, make sure you spell BRCA1 out in letters: bee-are-sea-aye-one!).
Where do BRCA1 and BRCA2 mistakes come from?
Most of the time germline genetic mutations are inherited, either from the father or the mother. (Yes, you can inherit breast cancer risk from your father!) While someone had to go first - this is called a de novo mutation - these genes are very stable and de novo mutations in the BRCA1 and BRCA2 genes are rare. You are very unlikely to be the first person in your family to develop a germline (heritable) mutation, although you may be the first person to get a BRCA-related cancer.
In some groups, such as the Ashkenazi Jewish population we know that the specific mutations, called founder mutations, have been passed down over hundreds even thousands of years.
How many people carry a BRCA1 or BRCA2 mutation?
It is estimated that in Australia 1 in 500 people carry a BRCA1 mutation and 1 in 225 people carry a BRCA2 mutation. These are called carrier frequencies and they vary depending on the population assessed.
There are other important genes that work with BRCA1 and BRCA2. The most important are:
- PALB2 (partner and localiser of BRCA2)
- BRIP1 (BRCA1 Interacting Protein 1)
- RAD51C and RAD51D
What happens if you inherit a BRCA1 or BRCA2 mutation?
Women who have inherited a BRCA1 or BRCA2 mutation have a very high lifetime risk of breast cancer (40 to 80%) and ovarian cancer (10 to 40%). Men who have inherited a BRCA1 or BRCA2 mutation have an increased risk of breast (6 to 7%) and prostate cancer (8 to 15%). The risk depends on which gene is damaged. People who have inherited a mutation in BRCA2 also have a small but significant risk of developing pancreatic cancer (<5% over a lifetime) and this risk is doubled if they smoke.
Why isn't cancer risk 100% if you are BRCA positive?
BRCA genes don't cause cancer, they actually prevent it! Everyone gets 2 copies of BRCA1 and 2 copies of BRCA2, one copy of each gene from each parent.
The second copy of the gene is working, so DNA mistakes can be fixed, protecting you from cancer.
You can’t have 2 mistakes in BRCA1, it's lethal and the babies don’t grow. A child that inherits 2 mistakes in BRCA2 usually has obvious deformities and the bone marrow doesn't work properly, a condition called Fanconi Anaemia.
Why do the cancers occur?
Over time, the random mistakes that occur in our DNA may damage or switch off the second copy of the BRCA gene. Now the cell has no recipe to make the spell checker that fixes the double strand breaks. The usual mistakes all cells make will build up much faster. That's why we see more cancers and cancers occurring at a younger age.
The risks are quoted as a range, even though no one gets 80% of a cancer. You can read about the actual risks measured in specific studies on the Cancer Genetics section of the Australian Government's Cancer Institute's eviQ website.
What to do if you carry a BRCA1 or BRCA2 gene mutation?
The mutation can be inherited from your mother or your father - the cancer risk is the same.
The BRCA1 or BRCA2 gene mutation doesn't skip a generation. Either you inherited the mutation present in your parent or you didn't. But, if you do carry a BRCA1 or BRCA2 mutation there's a lot you can do to reduced your cancer risk. Options included:
- starting breast screening earlier, using more sensitive imaging such as MRI
- surgery to reduce the lifetime risk to less than 1 or 2%
- taking risk-reducing medications
Some women, like Angelina Jolie, elect to have bilateral mastectomies. This is the most effective way to reduce breast cancer risk – the residual risk is tiny, less than 1 or 2% (compared to the 10 or 15% lifetime risk for the average Australian woman).
For women who don't have mastectomies but are 30 years or older annual breast screening with annual breast MRI +/- mammograms is recommended. The breast MRI’s are Medicare funded from age 30 to age 50, when many women switch to mammograms only. Screening before age 30 is rarely needed or recommended.
One of the most commonly used risk-reducing medications is Tamoxifen. Its made by Sandoz under the brand name Novolex-D. It's available on the PBS and generic forms are also available. It does have side-effects and some women who take it will still get breast cancer.
Angelina Jolie had her ovaries and fallopian tubes removed as well
There is no effective screening for ovarian cancer. The blood tests and ultrasounds are just not sensitive enough to detect the cancer before it has spread to the surrounding tissues. That is, it gives a false negative result. This type of screening is also associated with a high false positive rate (finding a lump that is not cancer) requiring surgical intervention and has been shown to be harmful.
Instead, if the risk is high, the ovaries and tubes should be removed when the risk approaches 1%. This is called a risk reducing salpingo-oophorectomy and is recommended at age 40 for a BRCA1 mutation carrier and age 45 for a BRCA2 mutation carrier. This surgery is even recommended in women in their 80s if they are fit and healthy.
What does a BRCA mutation mean for a man?
Men are also at increased risk of breast cancer. Screening is not required. Instead, if a man finds a lump in his breast, notices changes in the skin over the breast or has a nipple discharge, he should see his doctor.
Research has shown that if a prostate cancer develops in a man who carries a BRCA1 or BRCA2 mutation, it more likely to be aggressive and to spread (metastasise). PSA testing (the blood test that detects whether a prostate cancer is present) has been shown to help detect prostate cancers early in men with BRCA1 or BRCA2 mutations. PSA testing is recommended every year from age 40.
What about my children?
There is a 50% chance of a person who carries a BRCA1 or BRCA2 mutation, whether male or female, passing the mutation to their son or daughter. If a mutation is identified, then predictive testing would be available for adult blood relatives. This is Medicare-funded.
Genetic testing is not offered to children aged under 18. This is because it would not alter their management and destroys their right to medical autonomy. Instead, predictive testing is recommended at age 18, when starting a family or when screening would start: age 30 for women and age 40 for men.
Can I prevent the BRCA mutation being passed on to my children?
Yes. Some families use preimplantation genetic diagnosis (PGD) in the setting of in vitro fertilisation (IVF) to prevent the familial mutation being passed on to future generations. There's a 50% chance each time an egg or sperm is made that it carries the BRCA mutation and 50% that it doesn't. At the moment, we can't test the egg or the sperm without destroying it. Instead, at day 3 after fertilisation, one cell can be removed and the DNA checked. The family then uses the embryos that don't carry the mutation.
PGD + IVF can be expensive, is invasive and doesn't fit with everybody's ethics or religion. However, it can be very good news for families to know that even today we have techniques to prevent a mutation that has caused a lot of trouble and heartache in a family from being passed on.
What are the clues that you carry a BRCA1 or BRCA2 mutation?
BRCA mutations are more common in women with Triple Negative breast cancer. At diagnosis, the pathologist tests the cancer to see if the oestrogen receptor, progestrone receptor and/or the HER2 receptor is over expressed. A triple negative breast cancer does not over-express any of these 3 receptors. This testing guides treatment but is also a clue to inherited cancer risk.
If there is other family history, the affected woman will likely meet the Medicare criteria for bulk billed testing.
For women diagnosed with triple negative cancer at or before age 50, the likelihood she carries a BRCA mutation ~10%. Thus, under the eviQ guidelines, these women should be offered publicly-funded genetic testing if seen via a public familial cancer clinic, regardless of family history.
Women diagnosed with triple negative at an older age may elect to have BRCA testing, especially if they have a family history of BRCA-related cancers.
In addition to triple negative breast cancer, other clues to a BRCA1 or BRCA2 mutation, regardless of the individual’s current age include:
- Male breast cancer.
- Breast cancer diagnosed under age 40.
- Bilateral breast cancer with first diagnosis under age 50.
- Ovarian cancer: high grade serous, endometrioid or clear cell.
- Pancreatic cancer.
- Metastatic prostate cancer or prostate cancer before age 55.
- Jewish heritage and a history of breast, ovarian, prostate or pancreatic cancer.
More information and support groups
At Sydney Cancer Genetics, we are always happy to see individuals and families, either for testing to see if a BRCA1 or BRCA2 mutation is present or to discuss the implications and management if a mutation has already been found.
There are many support groups in Australia. Your local hospital probably has one. These are just a few national groups: