BRCA Testing: Genetic Testing For Breast Cancer

BRCA testing: Genetic testing for breast cancer

BRCA testing for breast cancer is useful to identify mutations in the BRCA1 and BRCA2 genes to assess the risk of cancer and sensitivity to therapies.

BRCA1 and BRCA2 are tumor suppressor genes that code for proteins, which play a role in ensuring the stability of cellular DNA.

These proteins are responsible for repairing any DNA damage that may occur.

However, mutations in these genes result in lowered production or improper function of the proteins.

Thus, such mutations have an association with an increased likelihood of developing genetic alterations that could lead to cancer. 

Though only 5 to 10% of breast cancer incidences are due to inherited mutations, breast cancer risk is substantial among women with germline BRCA mutations. BRCA testing will help in the risk assessment of breast and ovarian cancer, which is crucial for genetic counselling. Women who are at high risk for such mutations can undergo counseling for increased surveillance and/ or prophylactic surgeries. 

There are numerous studies that have been carried out to identify the penetrance of these genes among different populations.

The estimated cumulative risks among women of European ancestry for breast cancer vary between 45% and 85%, while that for ovarian cancer varies between 10% and 65% by age 70.

meta-analysis showed that BRCA1 mutation carriers had a 59% risk for breast cancer and 40% risk for ovarian cancer, while BRCA2 mutation carriers had 49% increased risk for breast cancer and 18% increased risk for ovarian cancer.

Are all BRCA mutations harmful?

There are certain inherited mutations in BRCA1 and BRCA2 genes that tend to increase the risk of female breast and ovarian cancers, as well as certain other cancers.

People inhering these mutations in BRCA1 and BRCA2 tend to develop breast and ovarian cancers at younger ages than people haven’t.

Breast Cancer Information Core has collected information on more than 1800 mutations in the BRCA1 gene and 2000 mutations in the BRCA2 gene.

This includes missense mutations, intronic changes, insertions, and deletions.

The different mutations confer differing risks for breast or ovarian cancer. The mutations are therefore classified as:

  1. strong and potential clinical significance
  2. unknown clinical significance
  3. benign or likely benign variants.

One may inherit the BRCA1 and BRCA2 mutations from either the mother or the father.

BRCA testing may be used to identify the predisposition for breast cancer; however, only about 5–10% of breast cancer cases are hereditary.

Among women who carry germline BRCA mutations, the risk for breast cancer is substantial.

BRCA testing and Therapy:

Apart from the increased risk of secondary cancers among individuals who carry certain mutations in the BRCA genes, there are other features of BRCA induced breast cancers. 

What are the types of cancers associated with BRCA mutations?

The following table is from the NHS foundation trust

GeneBRCA1BRCA2
Breast cancer in unaffected women (up to age 80)60–90%45–85%
Women with breast cancer (unilateral) Lifetime risk of a new cancer in the other breast50%50%
Lifetime risk of a new cancer in the other breast5 year risk of new breast cancer ~10%5 year risk of developing a new breast cancer ~ 5–10%
Ovarian cancer40–60%10–30%
Ovarian cancer lifetime riskRisk increases from age 40Risk increases from mid-late 40s
Male breast cancer, lifetime risk0.1–1%5–10%
Prostate cancer lifetime risk~10% Similar to population risk20–25%

Type of Breast Cancer 

BRCA1 mutation-associated breast cancers are found to be associated with a higher risk of triple-negative when compared with sporadic cases of breast cancer, while those associated with BRCA2 mutations are associated with an increased likelihood of estrogen receptor-positive breast cancers. 

Prognosis determination

BRCA testing cannot solely determine the prognosis, as age, type of therapy, and health status of the individual also play an important role.

However, the test can act as a complementary test, along with other determinants, to identify prognosis.

Management after BRCA testing

BRCA testing is useful to determine predisposition risk for breast cancer, prognosis and identify response to therapy.

Not everyone who carries a BRCA mutation is at an increased risk of breast cancer.

If an individual carries BRCA mutations, then increased screening should be carried out.

NIH (National Institute of Health), recommends the following screening schedule BRCA mutation carriers:

AgeAnnual mammographyAnnual MRI
30-39NoYes
40-49YesYes
50+YesBreast density

Being breast aware- Breast self-examination

In order to detect breast cancer early, women need to be breast aware.

This involves noticing changes that may occur in the breast.

Anyone can do a breast self-examination at home by feeling the breast with the palm of your hand.

It is best to do this examination once every month, about 5 to 10 days after the menstrual period.

If you see any noticeable changes, make sure to bring it to the attention of your medical practitioner.

Women who carry BRCA mutations have the option of deciding between increased screening, or they could opt for risk-reducing mastectomy. 

A risk-reducing mastectomy involves removing as much breast tissue as possible, which would reduce the risk of breast cancer by 90 to 95%.

BRCA testing is also useful to identify the risk of breast cancer associated with oral contraceptives usage and breast size.

Identifying the risk for breast cancer using BRCA testing will help in better managing lifestyle and diet to lower the risk of developing the condition.

 

Updated 25 July, 2020

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