BRCA1 and BRCA2 Mutations in Breast Cancer

The breast cancer susceptibility genes 1 and 2 (BRCA1 and BRCA2) are important tumor suppressors that code for proteins involved in cell regulation and the error-free repair of double-strand breaks (DSBs) in DNA.1 Mutations in BRCA1 and/or BRCA2 or other homologous recombination repair (HRR) genes result in homologous recombination deficiency and the inability to effectively repair DSBs.2-4 As a result, DSBs persist or are repaired via the error-prone NHEJ mechanism, resulting in genomic instability, accumulation of genetic alterations, and chromosomal abnormalities leading to carcinogenesis.

BRCA1 and BRCA2 mutations were the first HRR gene mutations discovered to be linked to breast and ovarian cancers.5 Historically, testing was used to identify BRCA mutations in unaffected family members to potentially provide an opportunity to take preventative measures.6 Hereditary mutations are associated with increased lifetime cancer risk.7 Today, BRCA1 and BRCA2 mutation status may also be a predictive biomarker for response to platinum-based chemotherapies and poly (ADP-ribose) polymerase inhibitors.1

Lifetime risk of breast cancer

Lifetime Risk of Cancer
Lifetime Risk of Cancer

Importance of Testing for BRCA1 and BRCA2 Mutations

Why Test

BRCA mutation status in unaffected family members can inform risk of developing breast and ovarian cancers.1,7 For patients with Stage IV breast cancer, biomarker testing is crucial for appropriate treatment selection.8

Whom to Test

While germline BRCA mutations are often associated with triple-negative disease, a majority of patients with germline BRCA mutations are hormone receptor (HR)-positive.1

NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®) recommend germline testing in patients with breast cancer8
NCCN Guidelines® for Breast Cancer: germline testing

Which patients with breast cancer should have germline testing?
Patients with recurrent or metastatic breast cancer

Which genes should be tested?
BRCA1 and BRCA2

BRCA1 and BRCA2 genes should also be evaluated for those meeting certain risk criteria for developing breast and ovarian cancers.6 See specific criteria for testing for familial risk below.

How to Test

Testing can be performed on blood, buccal mucosal swab, or tumor samples, the majority of which are formalin-fixed, paraffin-embedded samples.9,10 Tumor testing provides information on both germline and somatic mutations but does not distinguish between mutations. It is therefore inappropriate to draw any conclusions on familial risk based on tumor testing alone.11

Genetic/Familial High-Risk Assessment

Testing criteria in the NCCN Guidelines for Genetic/Familial High-Risk Assessment: Breast, Ovarian, and Pancreatic take into account age, personal cancer history, and family cancer history.12

Testing criteria for high-penetrance breast and/or ovarian cancer susceptibility genes (including BRCA1 and BRCA2) in the NCCN Guidelines12

Patients should be considered for testing for high-penetrance breast cancer susceptibility genes (including BRCA1 and BRCA2) if they meet any of the following criteria:

Personal cancer history

  • Diagnosed with breast cancer and any of the following:
    • Age ≤45 years
    • Age 46 to 50 years and has additional breast cancer primary or meets family history criteriaa
    • Age ≤60 years with triple-negative breast cancer
    • Meets family history criteriab
    • Has ≥2 additional diagnoses of breast cancer in patient and/or close blood relatives
    • Has ethnicity associated with higher mutation frequency (eg, Ashkenazi Jewish ancestry)
  • Diagnosed with other BRCA-associated cancerc
  • Has a BRCA pathogenic or likely pathogenic variant detected by tumor profiling on any tumor type without germline testing

Family cancer history

  • Is from a family with a known pathogenic or likely pathogenic BRCA variant
  • Has ≥1 first- or second-degree blood relative who meets testing criteria for high-penetrance breast cancer susceptibility genes (including BRCA1 and BRCA2) in the NCCN Guidelines

a≥1 close blood relative (first-, second-, and third-degree relatives on same side of family) with breast cancer at any age or prostate cancer, ovarian cancer, or an unknown or limited family history. b≥1 close blood relative (first-, second-, and third-degree relatives on same side of family) with breast cancer diagnosed at age ≤50 years, or ovarian, pancreatic, metastatic, intraductal/cribriform histology, or high- or very-high risk group (see NCCN Guidelines for Prostate Cancer13) prostate cancer at any age. cPersonal history of ovarian cancer, male breast cancer, exocrine pancreatic cancer, metastatic, intraductal/cribriform histology, or high-risk or very-high-risk group (see NCCN Guidelines for Prostate Cancer13) prostate cancer or prostate cancer of any risk group with family history (at least 1 of the following: ≥1 close blood relative [first-, second-, and third-degree relatives on same side of family] with ovarian cancer, pancreatic cancer, metastatic or intraductal/cribriform prostate cancer at any age, or breast cancer at <50 years of age; or ≥2 close blood relatives with breast or prostate cancer [any grade] at any age; or Ashkenazi Jewish ancestry).

Diagnostic Assays for BRCA1 and BRCA2 Testing

While Sanger sequencing is considered the gold standard for detection of genetic mutations, several next-generation sequencing platforms are available for the screening and identification of BRCA1 and BRCA2 mutations.10 Testing should include full gene sequencing, deletion/duplication analysis, and detection of known pathogenic/likely pathogenic variants in a Clinical Laboratory Improvement Amendments (CLIA)-certified and/or College of American Pathologists (CAP)-accredited genetic testing laboratory.14

The Myriad BRACAnalysis CDx® is a US Food and Drug Administration–approved option for assessment of deleterious or suspected deleterious mutation in germline BRCA1 and BRCA2.15

To optimize turnaround time and cost efficiency, some laboratories offer testing for BRCA mutations first, then automatically reflex to a larger multigene panel if the BRCA mutation test returns negative results.16

How to Interpret BRCA1 and BRCA2 Test Results

Sequence variations in BRCA1 and BRCA2 fall into 3 broad categories, single-nucleotide changes, small insertion or deletion events (indels), and large genomic rearrangements (LGRs).17 Single-nucleotide changes and indels can be detected by direct (Sanger) sequencing or next-generation sequencing. LGRs cannot be detected by direct (Sanger) sequencing. Instead, alternative polymerase chain reaction (PCR)–based techniques (eg, quantitative PCR, multiplex ligation-dependent probe amplification) are required.17

Whether performing in-house testing or sending to a testing lab, ensure the methodology is comprehensive and includes LGRs and indels17

Proper Interpretation of Test Results Is Critical for Informing Treatment Decisions

Many different mutations are possible in the BRCA genes; therefore, test results may not be a simple positive or negative.17,18

True Positive

Indicates:
A clinically actionable mutation has been identified, and the patient is BRCA mutation–positive18

May also be called:
Positive, pathogenic, likely pathogenic, deleterious, suspected deleterious19,20

True Negative

Indicates:
A specific deleterious familial mutation was known and tested for, but not found; the patient likely does not have a BRCA mutation18

May also be called:
Negative

Variant of Unknown Significance (VUS)

Indicates:
BRCA mutation was detected, but the specific variant has not been previously classified as harmful or harmless; the mutation has an unknown effect on protein function and risk of disease.17,18,21
Treatment decisions should not be made based on a VUS result.

May also be called:
Inconclusive or variant of uncertain significance13,16,18,19

Benign Variant

Indicates:
A BRCA sequence variant was detected, but the variant is nonpathogenic; the patient should be treated as BRCA mutation–negative20

May also be called:
Benign, likely benign, favor polymorphism, no mutation detected, negative19,20

Genetic Testing Process for BRCA1 and BRCA2

Meet with your multidisciplinary team to set up a standard testing protocol22
Multidisciplinary team collaboration can help streamline the testing process.22 Timely return of BRCA mutation test results is critical because these results can impact treatment decisions.23

BRCA Genetic Testing Process
BRCA Genetic Testing Process

Collaboration With a Genetic Counselor16,27-29

BRCA mutation testing, treatment, and patient counseling in breast cancer require communication between all members of the multidisciplinary team, including the important role of the genetic counselor.

Collaboration within the multidisciplinary team, including genetic counselors, is vital for making informed and appropriate treatment decisions.16,27-29

1. Tung NM, et al. Br J Cancer. 2018;119:141-152. 2. Frey MK, Pothuri B. Gynecol Oncol Res Pract. 2017;4:4. 3. Konecny GE, Kristeleit RS. Br J Cancer. 2016;115:1157-1173. 4. O’Sullivan CC, et al. Front Oncol. 2014;4:42. 5. Walsh CS. Gynecol Oncol. 2015;137(2):343-350. 6. Kuchenbaecker KB, et al. JAMA. 2017;317(23):2402-2416. 7. University of San Francisco. What is hereditary breast and ovarian cancer (HBOC) syndrome? Accessed November 15, 2019. https://kintalk.org/hboc/#_ftnref1. 8. Referenced with permission from the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®) for Breast Cancer V.2.2021. ©National Comprehensive Cancer Network, Inc. 2021. All rights reserved. Accessed March 12, 2021. To view the most recent and complete version of the guideline, go online to NCCN.org. 9. Ellison G, et al. BMC Clin Pathol. 2015;15:5. 10. Wu H, et al. Gene Ther. 2017;24(10):601-609. 11. Capoluongo E, et al. Semin Oncol. 2017;44(3):187-197. 12. Referenced with permission from the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®) for Genetic/Familial High-Risk Assessment: Breast, Ovarian, and Pancreatic V2.2021. ©National Comprehensive Cancer Network, Inc. 2020. All rights reserved. Accessed January 15, 2021. To view the most recent and complete version of the guideline, go online to NCCN.org. NCCN makes no warranties of any kind whatsoever regarding their content, use or application and disclaims any responsibility for their application or use in any way. 13. Referenced with permission from the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®) for Prostate Cancer V.2.2021. ©National Comprehensive Cancer Network, Inc. 2021. All rights reserved. Accessed February 17, 2021. To view the most recent and complete version of the guideline, go online to NCCN.org. NCCN makes no warranties of any kind whatsoever regarding their content, use or application and disclaims any responsibility for their application or use in any way. 14. Pal T, et al. Genet Med. 2020;22(4):681-685. 15. Myriad. BRACAnalysis CDx®. Accessed October 20, 2020. https://myriad-oncology.com/bracanalysiscdx/. 16. Stanislaw C, et al. Cancer Biol Med. 2016;13(1):55-67. 17. Wallace AJ. Eur J Hum Genet. 2016;24(suppl 1):S10-S18. 18. Committee on Practice Bulletins–Gynecology, Committee on Genetics, Society of Gynecologic Oncology. Obstet Gynecol. 2017;130(3):e110-e126. 19. BRACAnalysis CDx®. Technical information. Myriad Genetics Laboratories, Inc.; 2020. 20. Richards S, et al. Genet Med. 2015;17(5):405-424. 21. Miller-Samuel S, et al. Semin Oncol. 2011;38(4):469-480. 22. Leyland-Jones BR, et al. J Clin Oncol. 2008;26(34):5638-5644. 23. Smith KL, et al. Cancer J. 2011;17(6):492-499. 24. National Institutes of Health. Cancer genetics risk assessment and counseling (PDQ)–health professional version. Updated June 13, 2018. Accessed October 26, 2018. https://www.cancer.gov/about-cancer/causes-prevention/genetics/risk-assessment-pdq. 25. Hoogerbrugge N et al. Eur J Hum Genet. 2016;24(suppl 1):S19-S26. 26. National Collaborating Centre for Cancer. National Collaborating Centre for Cancer; 2013. 27. Senkus E, et al. Ann Oncol. 2015;26(suppl 5):v8-v30. 28. Lancaster JM, et al. Gynecol Oncol. 2015;136(1):3-7. 29. Eccles DM, et al. Ann Oncol. 2015;26(10):2057-2065.