Most breast cancers are not hereditary (caused by inherited cancer genes) and most women who get breast cancer don't have a family history of it.
If you have one female relative who developed breast cancer over the age of 40, your risk is unlikely to be very different from other women your age. However, sometimes breast cancer can run in families. In general, a family link is more likely when more members of your family have been diagnosed with breast cancer (or related cancers such as ovarian cancer). It is also more likely the younger they were when diagnosed and the more closely related they are.
Only a very small proportion of breast cancers (5 – 10%) are thought to be caused by a change (alteration) in a gene running in the family. The two genes that are most often found to be altered in hereditary breast cancer are called BRCA1 and BRCA2.
If a family has an altered BRCA1 or BRCA2 gene, usually several relatives on the same side of the family are diagnosed with breast cancer or related cancers. People in the family may also be diagnosed with cancers at a particularly young age.
BRCA gene alterations are more common in certain populations. If you have Ashkenazi Jewish ancestry and have relatives who've been diagnosed with ovarian or breast cancer, you may want to discuss your risk with your GP.
If you're concerned about your risk of breast cancer, visit your GP. They can talk to you about your family history and your risk.