While most breast cancers occur sporadically (usually linked to environmental factors such as smoking cigarettes and hormone replacement therapy), up to 10% are hereditary. Hereditary breast cancers are caused by DNA mutations that are typically passed down in families for generations. Features of hereditary breast cancers include a young age at diagnosis (under 50 years old), multiple affected relatives in multiple generations, individuals with more than one cancer, and relatives with related cancers such as male breast cancer and ovarian cancer. But how do these DNA mutations cause cancer?

DNA is our genetic code, our bodies blueprint on how to grow and function, and it is organized into segments called genes. Everyone has two copies of each of their genes, as one is inherited from the mother and one from the father. Our genes code for proteins that have a wide variety of roles in our bodies, including our physical traits, metabolism, immune system and organ function. Some of our genes, however, are responsible for keeping our cells from growing out of control and preventing the development of cancers. If one of these genes is mutated (mutation = damaging change), it may not be able to function properly, leading to an increased risk of cancers.

Identifying individuals who have a gene mutation leading to a hereditary form of breast cancer is important, as there are screening, treatment and risk reduction options that can be life-saving. While most people may be familiar with the BRCA1 and BRCA2 genes, which account for about half of hereditary breast cancers, there are over a dozen other genes that have been implicated in breast cancer risk, including genes such as ATM, CHEK2 and PALB2. Panel genetic testing that includes all of these genes and more is now available for individuals who meet medical criteria. If you think that you or a family member may warrant genetic testing for hereditary forms of breast cancer, speak with a genetic counselor or your doctor.