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Family Cancer History & Genetics

Family Cancer History And Genetics

People talk about how cancers “run in the family” and seem to pass from one generation to the next. Although many people think this is the most common cause of breast cancer, research shows that only an estimated 5-10% of breast cancers are hereditaryHereditary:
A trait, for example eye colour, that is transmitted genetically from one generation to the next. Some genetic mutations are inherited, for example mutations of the BRCA 1 or BRCA 2 genes that lead to a strong increase in the risk of breast cancer.
. However, if you have close family members who have been diagnosed with breast cancer, you may have an increased risk of developing the disease.

Signs Of Hereditary Breast Cancer

Family histories that may suggest an increased risk of breast cancer due to an inherited geneticGenetic:
Related to or caused by the genes.
abnormality include the following:

Gene Mutations

A gene which, when damaged (mutated), places a person at greater risk of developing breast and/or ovarian cancer, compared someone who does not have the mutation.
A gene which, when damaged (mutated), places a person at greater risk of developing breast and/or ovarian cancer, compared someone who does not have the mutation.
are genesGene:
A segment of DNA that contains hereditary information.
that normally help protect us from getting breast cancer. When there is a mistake, also known as a mutationMutation:
Any change in the DNA sequence of a cell. Mutations can be harmful, beneficial, or have no effect. Certain mutations may lead to cancer or other diseases.
, in one of these genes, an individual has a greater risk of developing breast cancer because the gene is not as effective at protecting the person from developing breast cancer.

We all have two copies of each gene, one that we inherit from each of our parents.  Normally these are two good copies.  However, if a parent has a BRCA1 or BRCA2 gene mutation, there is a 50% chance that the mutation will be passed down to their child. Inheriting a BRCA1 or BRCA2 mutation puts them at a greater chance of developing breast cancer during their lifetime.

 It is estimated that women who have inherited a BRCA1 or BRCA2 mutation have a 40-85% chance of developing breast cancer and a 20-40% chance of developing ovarian cancer in their lifetime. There are other inherited mutations of other genes that can also greatly increase breast cancer risk, but these are much less common than mutations in BRCA1 or BRCA2.

Genetic Counselling & Testing

Genetic counselling is offered when individuals and/or families are thought to possibly have a genetic risk of breast cancer. It is an important first step to determine the level of breast cancer risk and options to consider for breast cancer screening, ongoing assessment, and risk reduction. 

Genetic counsellorsGenetic counsellor:
A health care provider with specialized training and experience in the areas of medical genetics and counselling.
take a detailed personal and family cancer history and, sometimes with the help of computer software tools, estimate your breast cancer risk and the likelihood that you are a carrier of a genetic mutation that increases risk. If a genetic risk of breast cancer is suspected and you meet criteria, you will be offered genetic testing.

A blood test (or sometimes a saliva test) is required to test for genetic mutations that predispose an individual to breast cancer. The test usually looks for mutations in the BRCA1 or BRCA2 genes. Sometimes testing for less common mutations in other genes that are known to increase breast cancer risk is also done if appropriate.  There are many strategies that women found to have a BRCA1 or BRCA2 mutation can consider for reducing their risk of developing breast cancer and/or detecting cancer at a very early stage through screeningScreening:
The search for diseases such as breast cancer in people without symptoms. Mammography is an important tool for breast cancer screening and earlier detection.

Most women with a strong family history of breast cancer who have genetic testing will not be found to have an inherited gene mutation. Based on their family history, these women and their relatives are often still considered to be at increased risk and will be given appropriate recommendations for breast cancer screening and prevention based on that risk.

Reducing Your Risk

If you have a family history of breast or ovarian cancer, Canadian Breast Cancer Foundation encourages you to speak to a health care provider about your family’s cancer history, your breast cancer risk and if recommended, how to access genetic counselling and genetic testing, as well as options for screening for the earlier detection of breast cancer. 


Canadian Breast Cancer Foundation. (2010). Earlier Detection and Diagnosis of Breast Cancer: A Report from It’s About Time! A Consensus Conference. Toronto, ON: Canadian Breast Cancer Foundation. 

National Cancer Institute. BRCA1 and BRCA2: Cancer Risk and Genetic Testing. Accessed June 23, 2014.