Among all individuals with breast cancer, about 5 to 10% were born with a genetic risk for the disease. Genes are very small pieces of DNA that govern how cells work, including how and when they divide and grow. We inherit one copy of each gene from our mothers and one from our fathers. A mutation is a change in a gene that make it work differently than it should. Individuals with breast cancer may have one of these mutations.
Genetic testing can determine whether a hereditary gene mutation is present in an individual. This can help determine whether someone who has already been diagnosed with breast cancer has a higher risk of getting a second breast cancer, or other cancers.