Family history


Having a family history of cancer usually means that more than one close blood relative on the same side of the family has had cancer.

Cancer is a common condition. It is not unusual for more than one family member to develop cancer during their lifetime. Cancer can occur in more than one family member simply by chance or because of lifestyle or environmental factors.

Strong family history

The significance of a family history of breast cancer increases with:

  • the number of family members affected
  • the younger their ages at diagnosis
  • the closer the affected relatives are related to you.

The increase in risk is fairly small unless there are three or more first or second-degree relatives on the same side of the family with breast or ovarian cancer. It is important to note that a family history on your father’s side is just as important as it is on your mother’s side of the family.

The risk is stronger if two or more relatives have other characteristics associated with increased risk, such as being diagnosed before age 50 or being of Ashkenazi Jewish descent.

Although women who have one or more first-degree relatives with a history of breast cancer are at increased risk, most will never develop breast cancer. Of those women with a family history who do develop breast cancer, most will be older than 50 years when their cancer is diagnosed.

Despite the importance of family history as a risk factor, eight out of nine women who develop breast cancer do not have an affected mother, sister, or daughter.

Inherited genetic factors

Breast or ovarian cancer caused by inheriting a faulty gene is called hereditary cancer. We all inherit a set of genes from each of our parents. Sometimes there is a fault in one copy of a gene which stops that gene working properly. This fault is called a mutation.

There are several gene mutations that may be involved in the development of breast or ovarian cancer. The most common mutations are in the BRCA1 and BRCA2 genes. These are genes that normally prevent a woman developing breast or ovarian cancer. However, mutations in these genes increase a woman’s risk of developing breast cancer.

Ashkenazi is the term used to refer to Jews who have ancestors from Eastern or Central Europe, such as Germany, Poland, Hungary, Lithuania, Ukraine or Russia. As Ashkenazi Jews descend from a small population group, they have more genes in common than the general population.

While people of Ashkenazi Jewish descent don’t have any more faulty genes than anyone else, they do have a high prevalence of some gene faults and very low levels of others. Three gene faults associated with increased risk of breast and ovarian cancer have been found to be one of the genetic traits which are more common amongst Ashkenazi Jews than the general population. These gene faults occur in two per cent of Ashkenazi Jews compared to 0.2 per cent of the general population.

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