Hereditary Breast Cancer
Hereditary breast cancer or breast cancer that is driven by mutations in the genes is responsible for up to 10 per cent of breast cancers.
It can often be a very difficult form of cancer to deal with because women or men who are diagnosed may worry about other members of the family who could carry the high-risk genes.
The Genetic Health Service provides information and screening for hereditary breast cancer. Here the service's Sianan Keating answers questions about this type of breast cancer and genetic testing for the disease.
Who we are?
The Genetic Health Service of New Zealand is a national service that provides genetic diagnosis and advice and has three main Regional centres in Auckland, Wellington and Christchurch. We also attend many outreach clinics around the country. More information can be found on the Genetic Health Service website
Why would I be referred to the Genetic Health Service?
You or some of your relatives may have had cancer. The Genetic Health Service can help answer some of the following questions:
• Are members of my family at an increased risk of developing cancer?
• Can we have extra cancer screening?
• Is there anything I can do to reduce my cancer risk?
• Can I have a genetic test?
How common is inherited (familial) breast cancer?
• Breast cancer is the most common form of cancer affecting women. One in 9-12 women will develop breast cancer in their lifetime in the developed world.
• There are a number of recognised risk figures including hormonal, reproductive, obesity.
• The strongest risk figure is family history. Individual risk increases with an increasing number of affected relatives at a decreasing age of diagnosis.
• Most cases of cancer occur sporadically -Only 5-10% of breast cancer has a strong inherited component
The genetics of familial breast cancer
The familial proportion of breast cancer can be further broken down into cancers caused by known genes. We currently know and can offer testing in certain families for two main high risk genes, BRCA1 & BRCA2. Ongoing research is exploring the impact of other genes that may give carriers a low to moderate risk of developing breast cancer.
BRCA1 & BRCA2
BRCA1 and BRCA2 are both tumour suppressor genes. This means they have a protective role in preventing cancer from developing. Cancer development is a complicated process involving several other genes and environmental factors. If there is a gene fault in BRCA1 or BRCA2, the gene can no longer function normally and there is higher than normal chance that a tumour may develop, and usually at a younger age.
We all have two copies of each BRCA gene, as we do all our genes. If an individual has fault in one copy of a BRCA gene, this is enough to give them a predisposition to develop cancer. When we have children, we pass on only one copy of each of our genes to the child, and they receive the other copy from their other parent. Therefore, if an individual carries a BRCA gene fault, there is a 50:50 or 1 in 2 chance that they will pass that copy of the gene onto each child.
Figures can vary but we quote that a woman with a BRCA gene change will have a 50-85% lifetime risk of developing breast cancer, and a 20-40% lifetime risk of developing ovarian cancer (the BRCA 2 risk tends to be lower than the BRCA1 risk). This is compared with the general population risk of approximately 10% for breast cancer, and 1.6% for ovarian cancer. There may also be a slightly increased risk for men with a BRCA 2 gene change, of male breast and prostate cancer. Associations have also been made between gene faults in BRCA 1 and 2 and an increased risk of other cancers, including pancreatic cancer. However the risk of these cancers is still generally small and there are no effective screening recommendations. It is important to note that risk estimates can vary depending on the family history, and not everyone with a BRCA mutation will develop cancer.
Is it likely that the cancers that have happened in my family are due to BRCA1 or BRCA2?
To decide whether cancer diagnoses are likely to be due to an inherited predisposition we take a detailed family history from patients. Cancer is common, particularly in older people. Most of these cancers will have occurred by chance. From your family tree, we look at the types of cancer in your family and the ages of diagnosis. Only a small number of families have a strong inherited tendency to cancer. This is more likely when we see:
• Several relatives with the same types of cancer, or cancers which are associated (e.g. breast and ovary or bowel and womb)
• Individuals with cancer at young ages
• Individuals with more than one primary cancer
• Certain cancers (e.g. lung and cervical) have recognised environmental causes and tend not to be inherited.
What about screening?
In some families due to a significant family history of breast cancer we may recommend individuals receive additional screening. Cancer screening aims to detect cancers early when the outlook following treatment is usually good. All types of cancer screening have drawbacks. It is important that extra screening is only offered when the benefits to an individual outweigh the risks.
Can I have a genetic test?
Genetic testing is only possible in a small number of families. In these families we usually require a blood sample from a relative with cancer before testing can be considered in other family members.
How can I be referred to the Genetic Health Service?
The best way to find out if a referral to our service would be appropriate is to visit your GP, who would be able to tell you if you meet our guidelines and refer you if appropriate.