What you need to know

In breast cancer, there are two types of genetic testing. One is used primarily in healthy people to identify specific gene mutations that have high risk for cancer and inherited.

This is to predict the risk of having breast cancer in the future. These genetic tests can also be used in people with cancer to determine if they possess these hereditary mutations. The European Commission Initiative on Breast Cancer (ECIBC)'s quality assurance scheme for breast cancer services states that centres must offer access to genetic testing and counselling for all women diagnosed with breast cancer who are at a high risk of having genetic mutations.

The second type is genomic testing, which is performed on the breast tumour tissue to determine the genetic "signature" of a cancer to provide information relevant to possible treatment approaches.

For example, the ECIBC's European Guidelines on Breast Cancer Screening and Diagnosis suggests using genomic testing to guide use of chemotherapy in women whose breast cancer meets certain characteristics.

Hereditary Breast Cancer

About 5 to 10% of breast cancers are considered to be hereditary. Abnormalities (or mutations) in two genes in particular, BRCA1 and BRCA2, account for most high-risk hereditary breast cancers. BRCA1/2 mutations are uncommon and cause about 3% of breast cancers overall (and 10 to 15% of ovarian cancers).

Yet they are responsible for the breast cancer cases in nearly half of all families with multiple cases of breast cancer and up to 90% of families with both breast and ovarian cancer. The cumulative breast cancer risk to the age of 80 years is estimated to be 72% for BRCA1 and 69% for BRCA2 mutation carriers.

There are other higher risk mutations, such as in TP53 and CHEK2, which are rare but are included in familial breast cancer management.

There are at least 200 other genetic variants associated with a low risk of breast cancer. In certain combinations, they could be responsible for additional breast cancers. 

In Healthy People

Genetic risk testing should be performed in national health services and breast cancer services/centres according to the latest evidence-based guidelines, with access to genetic counselling and informed consent. Tests are carried on a blood sample, or a sample from the mouth or saliva. 

In healthy people, testing for BRCA1/2 and certain other mutations is only indicated when there is a high index of suspicion, such as a mutation identified in a close relative with breast cancer, or a broader family history of breast cancer. 

Certain groups such as women of Ashkenazi Jewish descent, those with breast cancer at a younger age (5 years or younger), and those with triple-negative breast cancer are more likely to have BRCA1/2 gene mutations and can be offered genetic testing. Any direct-to-consumer tests must be used with the appropriate caution, and include informed consent, counselling and medical supervision.

In Women With Breast Cancer

Among women with breast cancer, the St. Gallen 2021 meeting recommendations concluded that genetic panels for hereditary cancer should be offered to women if they have a more than 10% risk for a hereditary mutation in algorithms based on family history, age at diagnosis, and tumour subtype. Testing should use a gene panel including BRCA1 and 2, ATM, BARD1, BRIP1, CDH1, CHEK2, NBN, PALB2, PTEN, STK11, RAD51D, and TP53.

In women with metastatic breast cancer, identifying a BRCA mutation may make them candidates for some more novel therapies. 

In the ECIBC requirements for breast centres, all women diagnosed with breast cancer and with a high risk of genetic mutations must be offered genetic counselling and have unrestricted access to genetic testing.

Genetic Testing of Tumour Tissue

Tumour samples can be tested for mutations that guide prognosis and treatment decisions, as a complement to the standard pathological evaluation. 

These include gene array panels or gene expression profiles. For examples these can help indicate whether to use chemotherapy before or after surgery to reduce the chances of recurrence, or to identify genes that can be targeted with biological drugs and different combinations of therapies. 

Types of Genomic Molecular Assays

Gene or genomic signature tests of tumour tissues have been widely studied in clinical trial to identify their predictive value and are gradually becoming available for wider use. These prognostic assays can indicate, based on a high-risk score, whether or not a woman with ER-positive and HER-negative tumour and other specific characteristics would benefit from chemotherapy before or after surgery (or those with a low risk who maybe spared chemotherapy). Other tests indicate who might benefit from extended endocrine therapy. Some of these tests include: Oncotype DX, MammaPrint, Breast Cancer Index, EndoPredict and Prosigna.

The ECIBC's European Guidelines on Breast Cancer Screening and Diagnosis recommend using a 21-gene recurrence score in women with endocrine-receptor positive, HER2-negative, lymph node negative or up to 3 lymph nodes positive invasive breast cancer to guide the use of chemotherapy. They suggest using the 70-gene signature test only for women with high clinical risk of cancer recurrence.