Most cases of breast cancer are not related to an increased risk due to family history. However, about five to fifteen in every 100 women with breast cancer have a family history which is likely to have contributed to why they developed the disease. At least 10 in 100 men with breast cancer also have a family history of the disease.
It’s not easy to give a single definition of a family history of breast cancer, because there are many different patterns. However, you might have an increased risk of developing the disease if:
- several blood relatives in your family have had breast cancer or ovarian cancer.
- or, you have blood relatives who were diagnosed with breast cancer at a relatively young age (e.g. under 40).
However, because breast cancer is a common disease, having one relative diagnosed over the age of 40 is not unusual and would not normally suggest that other family members are at increased risk. It’s important to look into any patterns of other cancers in the family too, because in some cases these can also indicate an increased risk of breast cancer in the family.
If you do have a family history, it doesn’t mean you will definitely get breast cancer, but it does mean your risk may be higher than for people without a family history. It may also mean you could develop breast cancer at a younger age.
About 90 (estimates vary from 85 to 95) will not have a significant family history. About 10 will have a family history that may explain why they developed breast cancer. Of these:
About five will have a fault in a gene known to be linked to breast cancer (eg BRCA1, BRCA2 or TP53)
About five will have no known genetic reason for their family’s increased risk
Gene faults and family history
Sometimes, faults in particular genes (such as BRCA1, BRCA2 and TP53) explain why a family has an unusually high number of relatives who have been diagnosed with breast cancer. About half of all women with a family history of breast cancer who have been diagnosed with the disease have a fault in a gene known to be linked to breast cancer, such as a BRCA1, BRCA2 or TP53. In the other half, the reason for their family’s increased risk of breast cancer is not known.
The BRCA1 and TP53 genes are found in everyone. BRCA genes play an important role in repairing damage to the DNA in our cells, while the TP53 gene normally controls when a cell divides.
When a fault occurs in one of these genes it can no longer function properly, resulting in DNA damage and uncontrolled cell growth which can lead to a cell becoming cancerous.
As well as increasing the risk of breast cancer, BRCA gene faults can increase the risk of some ovarian cancers too, which is why we mention both breast cancer and ovarian cancer when describing a family history. Gene faults also explain some cases of breast cancer in men too.
Even if a faulty gene is identified in a family member, this doesn’t mean that all other family members are at risk. Some (but unlikely all) family members may have inherited the gene from a parent, if they carried it. There is a 50:50 chance that a faulty gene will be passed from a parent (whether male or female) to their child.