Genetics and Breast Cancer

Cancer is a common illness, and there are people affected by it in most families. The majority of cancers are caused by a combination of factors, including environment, lifestyle and genetics. In some cases, genetics and breast cancer can be linked. In fact, genetic predisposition to breast cancer is identified in about 10% of cases.

Genes contain the instructions for all our body parts and functions. Our genes have variants, some of which disrupt the function of the genes, which, in turn, can cause genetic disease. These are called pathogenic variants or genetic mutations.

Certain variants (sporadic or acquired) occur naturally in some of our cells over our lifetime and are not usually passed on to our children. Other (hereditary) variants are passed on by our father or mother at conception and are found in every cell in our body. Hereditary variants have a 50% risk of being passed down to children, creating a potential link between genetics and breast cancer.

If you have questions about genetics and breast cancer risk, please contact Nathalie Bolduc, Certified genetic counsellor, at nbolduc@rubanrose.org.

A hereditary predisposition to cancer in the family may result in:

• Cancer occurring at a younger age than in people with sporadic cancers (e.g. before the age of 50)
• More than one cancer in the same person, of the same type or not (e.g. having breast cancer twice, or breast cancer and ovarian cancer)
• Rare cancers, such as ovarian cancer or male breast cancer
• Multiple members of the same family with the same type of cancer

Both men and women can carry a pathogenic variant in a cancer predisposition gene. Inheriting a genetic mutation does not necessarily mean that you will develop cancer. Rather, it means that, depending on the gene, your risk of developing certain types of cancer is higher than that of another person of the same age. Other risk factors, such as age, lifestyle and environment, also contribute to the development of cancer.

Several genes are currently known to predispose their carriers to breast cancer: BRCA1, BRCA2, PALB2, CHEK2, CDH1 and ATM. Research will identify other genes over the coming years.

Talk with your doctor if you have questions or concerns about your risk of developing breast cancer because of a hereditary predisposition. Your doctor can refer you to a genetics service in your area to meet with a genetics specialist (for example, a genetic counsellor or geneticist).

During a genetic counselling session, a specialist will assess your risk based on your medical and family history and determine if you are eligible for genetic testing. You’ll have the opportunity to learn about the benefits and drawbacks of genetic testing as well as the options for management, testing and treatment.

This information will help you decide whether or not to pursue genetic testing. The decision to undergo genetic testing is a very personal one. If you do not go ahead with testing, other options for screening and management may be available once your personal and family cancer history has been assessed.

If you are a carrier of a genetic predisposition to breast cancer, you should know that each gene is associated with an increased risk for different types of cancer in both women and men. Guidelines are available to determine what screening or risk reduction options you have, at what age to start them and how often to do them.

Precision medicine aims to establish customized screening, prevention and treatment strategies for patients, depending on their environment, their lifestyle and their tumour’s genetic and biological profile.

Several experts in Quebec specialize in precision medicine. Over the last few years, The Foundation has invested close to $1.5M to support these four research projects:

• Jacques Simard: PERSPECTIVE study on personalized risk stratification for prevention and early detection of breast cancer
• William Foulkes: Breast cancer genetics among the Quebec population: twenty years after BRCA1/2
• Mark Basik: Discovery of two tumour suppressor genes, ARID1A and SPEN, in hormone-sensitive breast cancer
• Patricia Tonin: evaluating the possibility that women carrying the genetically high-risk BRCA 1/BRCA 2 genes, or their family members, may carry more than one genetic mutation.

Assessing the genetic markers of a person’s tumour, as well as its protein profile and its surrounding environment will enable the medical and scientific community to customize this person’s individual risk of developing breast cancer, to help in the diagnosis, to plan the treatment that will be most effective, as well as to reduce the toxicity of side effects by allowing the use of less invasive treatments. Ultimately, this medicine aims to improve the survival rate and the quality of life of cancer patients.