According to what we know now, only 5 to 10% of breast cancers in the United States are linked to an inherited gene mutation. Of those, half are linked to abnormal structural changes in the BRCA1 or the BRCA2 gene, both of whose functions are to repair damaged DNA by making proteins that act as tumor suppressors. When a mutation of this type is passed down, it can pave the way for out-of-control cell division leading to a greatly increased risk of breast and/or ovarian cancer.
To be clear, the vast majority of breast cancer patients do not carry any of these transmitted mutations. However, when a patient has a strong family history of breast cancer, and comes from certain susceptible racial or ethnic populations, genetic tests exist that can confirm or rule out this hereditary aspect of the disease. These tests are usually done on a blood or saliva sample and sent to a commercial lab. Though some women decide on their own to be tested prophylactically in order to identify and manage possible future cancer risk, it is imperative to seek counsel from one’s health care provider before making the decision of whether to undergo genetic testing or not.