Genetics of Breast Cancer

According to the National Cancer Institute (NCI), the lifetime risk for a woman to develop breast cancer is 12.8 percent or one in eight, while the lifetime risk to develop ovarian cancer is a little greater than 1 percent (1.5 percent or one in 67).

Approximately 5 percent to 10 percent of breast and ovarian cancers are due to known predisposing genetic factors. This means that the majority of breast and ovarian cancers are, in fact, not inherited.

A gene is a basic unit of heredity that determines a person’s traits. Genes are located on one of the 46 chromosomes housed within cells that make up all of the tissues of the body. They come in pairs, and work together to make proteins. One member of the gene pair is inherited from the mother, and one from the father.

Cancers develop due to alterations (mutations) in genes. When an alteration or mutation in a gene is present in the eggs and sperm, also called germ cells, it is referred to as a “germline mutation.” When a germline mutation is inherited it is present in all body cells.

Only a small percentage of cancers involve inherited mutations that are passed from generation to generation. The majority of cancers can be attributed to acquired mutations. “Acquired” means that the mutations occur only in the tissue that is affected by cancer and are not present in all cells of the body. Acquired mutations are not inherited and are not passed down to our children.

Listed below are several genetic syndromes associated with an increased risk for breast cancer that require clinical care by a physician or other healthcare professional.