Just how are genetics and breast cancer connected? Genetic counsellor, Sarah Walters, explains this frequently asked question.
The comment I always think about is that ‘all cancers are genetic, however, not all are inherited’. This statement manages to confuse people for a while, as we think that we can only get faulty genes from our parents. But cancers also occur when something goes wrong in our genetic material (DNA) at any time during our lifespan.
The purpose of genetic counselling is to untangle the family history and the genetics, and to make some sense out of what is going on. As a genetic counsellor, I either meet with people who have a family history of breast and/or ovarian cancer, but do not have cancer themselves, or with people who have been newly diagnosed, who are looking for answers.
We often hear about the BRCA1 and BRCA2 genes causing breast and ovarian cancer in the media, but there is so much more to these two cancers. There are many other genes related to cancer, which may have a small, but cumulative effect on causing the cancer.
An important component of genetic counselling is recording an accurate and comprehensive family history. Only when people see their families drawn out on paper, do they realise how many family members there are, and how many have been affected by cancer. When seeing a genetic counsellor, it is vital to take along as much information on any cancers in the family, irrespective whether you think they’re related or not, e.g. prostate cancer. Cancer history from both sides of the family is essential. From these family trees, patterns may emerge and shed some light on the cancers in the family.
Education plays a major role in genetic counselling. It is estimated that 90% of cancers are not inherited and that between five and 10% of breast/ovarian cancers are caused by an inherited genetic fault. Genetic counsellors search for signs, such as age of onset of cancer in a particular individual or whether a cancer appears in paired organs (both breasts or ovaries). We also look for unusual cancers, such as breast cancer, in a male individual.
When faced with a request for BRCA1/2 testing, the frequently encountered challenge and incorrect perception is that it only requires a blood sample to obtain a simple positive/negative result. This result will then indicate the presence or absence of an inherited risk for breast/ovarian cancer. However, over a thousand different mutations in BRCA1/ 2 have been reported.
Mutations (or changes in the DNA code) occur throughout the genes. Some of these changes may be pathogenic (causing disease) and some may be benign (thought to not cause disease). There are some changes in the DNA that no one currently knows whether they’re pathogenic or benign, as not enough information is currently available. Only time will tell when more research has been collated.
What makes things more confusing is that BRCA1/2 genetic testing is not a diagnostic procedure. However, it can help determine lifetime risk in mutation carriers. Mutations may be inherited, but this does not automatically mean that you definitely will develop cancer. Your risk may increase, but by how much may depend on the mutation and which gene has the fault. An inherited mutation in a BRCA1/2 gene may increase your risk of breast cancer to about 80%, and the risk of ovarian cancer to around 60%. These risks may be gene and family specific. Increased risks may give the individual access to options for management of these cancer risks, by increased monitoring, preventative surgery and/or medication.
Founder effects have led to some specific mutations being common in certain populations of defined geographical or ethnic background, e.g. individuals of Ashkenazi Jewish descent or Afrikaner descent. Triple-negative breast cancer (ER-. PR-, HER2-) is regularly reported to be three times more common in women of African descent and in premenopausal women. Triple-negative breast cancer represents 10% to 20% of invasive breast cancers. Finally, one mutation was identified in Cape Coloured and Xhosa women, which makes it a frequent founder mutation in the Western Cape province.
A crucial aspect of genetic testing, which must be determined before sending in blood for testing, includes deciding which is the appropriate and most applicable breast/ovarian cancer genetic test in a particular family (e.g. related to specific population groups and gender considerations such as males with breast and/or prostate cancer etc.); and what the costs will be, in order for patients to be prepared for any upfront financial commitments, or whether their medical aids will fund these tests.
Pre-test genetic counselling is valuable in explaining the nature of the information obtained and the limitations of the genetic testing. Genetic counsellors are experienced specialists in the coordination of any genetic testing matter, advising patients and communicating with their physicians.
There are several genetic counsellors situated in some major cities across the country. Ask your doctor to put you in contact with your local genetic counsellor for a comprehensive assessment regarding genetic testing and access to accurate and appropriate testing.
Written by Sarah Walters.