Family history as a risk factor for breast cancer

A positive family history is the strongest predictor of a woman developing breast cancer. The more family members diagnosed, the closer their relationship and the earlier the age of onset, the higher the chance of other women in the family also developing the disease.

It is estimated that approximately 20 to 30% of all breast cancer patients have at least one 1st degree relative with the same condition and 5 to 10% of patients have a strong genetic predisposition (more than one relative with breast cancer).

The following factors increase the risk of a woman developing breast cancer:


  • number of family relatives affected by breast or ovarian cancer,
  • ratio of affected to non-affected individuals,
  • how closely related affected relatives are,
  • the age of onset of the disease,
  • whether the breast cancer affects one or both breasts (bilateral disease),
  • the incidence of male breast cancer in the family.

The number of these elements determines whether the risk is high, moderate or low. We also use this data to identify families in whom it may be useful to perform genetic analysis.

The criteria used for genetic analysis are shown in Table 1. These only tend to act as guidelines because occasionally the analysis is also performed in families which do not strictly meet the criteria. For example, if extenuating circumstances exist, such as a family tree that is difficult to assess (a small family or one that includes a large number of male relatives) or where there are significant clinical implications of a positive result. An exception may also be made in the case of extremely anxious patients for whom a genetic test is the only source of reassurance.

Table 1: Inclusion criteria for molecular genetic analysis of the BRCA1 and BRCA2 genes:

  • families with three first degree relatives* affected by breast and / or ovarian cancer.
  • families with at least two first and / or second degree relatives ** with breast and / or ovarian cancer occurring in patients who are younger than 50 years of age.
  • all patients who develop breast and / or ovarian cancer before the age of 35.
  • relatives belonging to a family in which the mutation has been identified.
  • male patients with breast cancer.

* First-degree relatives: mother, daughter or sister
** Second-degree relatives: grandmother, grandchild, aunt or niece