Genetic Testing for Breast Cancer: What You Should Know

January 25, 2018

Many factors contribute to increased breast cancer risk for some women — including certain inherited genes. About 5 to 10 percent of breast cancer cases are thought to be hereditary, meaning that they are the direct result of gene mutations passed on from a parent.

Genes are individual units of inheritance made of DNA. There are two copies of each gene, which are inherited from each of our parents. Genetic testing looks for alterations in a person’s genes, which can result in an increased risk of developing some cancers — including breast cancer.

The standard practice for genetic testing at Dana-Farber’s Center for Cancer Genetics and Prevention typically involves a multi-gene panel test that can test people for 40 or so genes that indicate a hereditary cancer risk. This includes the genes BRCA1 or BRCA2, the most common causes of hereditary breast cancer in women, as well as other genes that might not have a family history component.

“What we’re learning is that there are a number of other genes that increase the risk of breast cancer, but not necessarily to same magnitude as BRCA1 or BRCA2, where family history would not necessarily be indicative of mutations that are present,” says Huma Q. Rana, MD, Clinical Director of Cancer Genetics and Prevention at Dana-Farber.

Most people who develop breast cancer have no family history of the disease. However, if a person has a strong family history of breast and ovarian cancer, it is possible that they have inherited a BRCA1 and BRCA2 gene mutation, which sharply increases a woman’s chances of developing breast or ovarian cancer, often at an early age. A woman with a BRCA1 or BRCA2 mutation has about a 7 in 10 chance of getting breast cancer by age 80, according to the American Cancer Society.

Huma Q. Rana, MD, Clinical Director of Cancer Genetics and Prevention at Dana-Farber.
Huma Q. Rana, MD, Clinical Director of Cancer Genetics and Prevention at Dana-Farber.

If a person has a BRCA1 or BRCA2 gene mutation or another “high-risk” gene mutation like TP53 or PALB2, they have a number of options to reduce their breast cancer risk – including more frequent breast exams, early breast imaging and screening, and preventative mastectomies. Other genes of “moderate risk” that can appear in a multi-gene pane test include CHEK2 and ATM, which are also inherited, but are associated with more attenuated risks as compared to BRCA1 or BRCA2.

Family history of cancer can signal the presence of these genes and gene mutations in people, but it is still an imperfect indicator, Rana says. While conducting extensive gene testing, researchers have discovered there is a larger spectrum of people who have high-risk gene mutations than previously thought. As a result, researchers are now exploring how to effectively screen these people.

A study at Dana-Farber currently uses new whole body magnetic resonance imaging (MRI) technology in patients with Li Fraumeni syndrome, which is caused by a mutation in the TP53 gene and may lead to a predisposition to many cancers, including those of the breast, brain, blood, or bone.  The data so far suggests that people with TP53 mutations who have this more intensive screening have a higher survival rate, Rana says.

Doctors and cancer genetic counselors, like those who work with patients in Cancer Genetics and Prevention at Dana-Farber/Brigham and Women’s Cancer Center, can educate patients about the implications of carrying a genetic risk for breast cancer, including screening recommendations.