Let’s start with some basic concepts:
What is hereditary cancer?
Cancer is a common disease and most cases are associated with a combination of factors, including genetics, lifestyle and the environment. Cancer develops in our cells when genetic changes (acquired during our lifetime) disrupt the control of their division and these abnormal cells do not die as they should.
The majority of cancers are therefore not hereditary. However, some people are born with a change (called a pathogenic variant) in a gene known to be associated with a particular type of cancer. These individuals are at greater risk of developing certain types of cancer than the rest of the population.
However, it is a “predisposition” and other risk factors, such as age, lifestyle and environment, also contribute. Therefore, not all individuals who carry a pathogenic variant in one of these genes will develop cancer.
How are these genes transmitted?
Usually, each person has two copies of each gene in each of their cells: one from their mother and one from their father. The majority of genes associated with cancer predispositions follow an autosomal dominant inheritance. It means that :
- An at-risk individual has one copy of the BRCA1 gene (or another gene) that is functional but the other copy has a pathogenic variant that prevents normal function of the gene.
- The disease affects both men and women.
- The probability of passing this variant to your children is 50% (1 in 2), regardless of the number of children that you have.
- It does not “skip” a generation. So if neither parent has this pathogenic variant, neither will their children.
Is hereditary cancer common?
Approximately 5-10% of cancers are associated with hereditary predisposition. However, this proportion varies depending on the type of cancer. A few examples: around 10% of breast cancer is associated with a genetic predisposition while this proportion is around 20% for ovarian cancer. Approximately 5 to 10% of colon cancers and of prostate cancers have a hereditary cause.
Nathalie Bolduc, MSc, CGAC, CGC
Certified Genetic Counsellor