How do I conduct BRCA testing?

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Germline vs somatic mutations

Testing for germline BRCA1/2 mutations has been available since the 1990s and is currently used to assess cancer risk and inform treatment decisions. More recently tumour testing for BRCA mutations has also become available.1,2

A BRCA mutation can be either germline or somatic.3,4

  • A germline mutation occurs in a sperm cell or an egg cell and is passed directly from the parent, hence this type of mutation can be inherited, and therefore, can inform familial risk. These mutations become incorporated into the DNA of every cell in the body of the offspring. Although not everyone with a gBRCAm will have a family history of BC, there is the risk that it can be passed onto a carrier’s offspring5
  • A somatic mutation is a spontaneous genetic alteration that a cell acquires after conception. This type of mutation can develop in any cell in the body except the germ cells. This is a non-inheritable mutation6

With germline testing, variants in a patient’s germline that can be passed on to offspring can be identified.3,7 Germline mutations can be identified by analysing DNA in a blood or saliva sample.2 Germline mutations are found in ~6% of patients with breast cancer.5,8

Determination of a mutation being somatic in origin requires genetic profiling of cancer tissue and a positive tumour test result, as well as analysis of DNA from blood or saliva to rule out germline mutations.2,7 These mutations are found in ~3% of patients with breast cancer.9

Evolution in Genetic Testing for Breast Cancer
Evolution in Genetic Testing for Breast Cancer

Blood germline testing

A blood sample is taken from the patient and sent to an internal or external lab for DNA extraction. The DNA is processed and tested to determine the presence of germline BRCA mutation(s).10

The field of genetic testing for breast cancer has evolved over the years. Originally single genes were sequenced, which was labour intensive and expensive.11 With the advances in next generation sequencing technology (NGS), multigene panels have been introduced, allowing for wider genetic assessment, a faster testing process, with higher throughput, without being cost prohibitive.12

Evolution in Genetic Testing for Breast Cancer
Evolution in Genetic Testing for Breast Cancer

Newer gene panels are being developed, which contain other cancer susceptibility genes. These panels differ in the genes they include, and can, In some cases, be customisable.12 For example, a gene panel for the Homologous Recombinant Repair pathway genes will contain BRCA1 and BRCA2, alongside other cancer-related genes, including PALB2 and CHEK2.13

Evolution in Genetic Testing for Breast Cancer
Evolution in Genetic Testing for Breast Cancer

Tumour Testing

Molecular testing of tumour samples can be utilised to identify genetic changes in cancer cells that may be driving the growth of an individual’s cancer. Initially, tumour testing posed challenges since it proved difficult to conduct accurate gene sequencing from formalin fixed paraffin embedded (FFPE) tissue samples.10,14 With the advances in NGS, FFPE tissue can now also be reliably used for molecular testing.16

Tumour testing detects both somatic and germline mutations but does not typically distinguish between them thus a follow-up germline test is required to determine if the mutation is inherited.7,17

The utility of tumour testing is growing as more targeted therapies are developed. Limited-gene and multi-gene panels are also employed in tumour testing.17

BRCA, breast cancer gene; gBRCAm, germline BRCA mutation; DNA, deoxyribonucleic acid; CDH1, cadherin 1; CHEK2, checkpoint kinase 2; NGS, next generation sequencing; PALB2, partner and localiser of BRCA2; PTEN, phosphatase and tensin homolog; RNA, ribonucleic acid; TP53, tumour protein p53.

References:

  1. Frey MK et al. Gynecol Oncol Res Pract. 2017; 4:4.
  2. Robson ME et al. J Clin Oncol. 2010; 28: 893-901.
  3. Griffiths AJF et al. An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman; 2000. Somatic versus germinal mutation. Available from:
    https://www.ncbi.nlm.nih.gov/books/NBK21894/. [Accessed February 2021].
  4. Neff RT, Senter L and Salani R. Ther Adv Med Oncol. 2017; 9: 519-531.
  5. National Cancer Institute. NCI Dictionary of Terms – germline mutation. Available at:
    https://www.cancer.gov/publications/dictionaries/cancer-terms/def/germline-mutation [Accessed February 2021].
  6. National Cancer Institute. NCI Dictionary of Terms – somatic mutation. Available at:
    https://www.cancer.gov/publications/dictionaries/cancer-terms/def/somatic-mutation [Accessed February 2021].
  7. Robson, ME et al. J Clin Oncol. 2015; 33: 3660-3667.
  8. Tung N et al. J Clin Oncol. 2016; 34: 1460-1468.
  9. Winter C et al. Ann Oncol. 2016; 27; 1532-1538.
  10. Capoluongo E et al. Semin Oncol. 2017; 44: 187-197.
  11. Kamps R et al. Int J Mol Sci. 2017; 18: 308.
  12. Lynce F and Isaacs C. Am Soc Clin Oncol Educ Book. 2016; 35: e72-e78.
  13. Tavtigian SV. Homologous Recombination Repair Genetics (HRR genes). Available at:
    https://uofuhealth.utah.edu/utah-genome-project/projects-list/breast-ovarian-pancreatic-cancers.php [Accessed February 2021].
  14. Normanno N et al. J Cell Biochem. (2013) 114:514–24.
  15. Kapoor N. How Do Single-Gene & Multi-Gene Tests Compare? Available at:
    https://www.breastlink.com/blog/nimmi-s-kapoor-md-gene-tests-asbs/ [Accessed February 2021].
  16. McDonough SJ et al. PLoS One. 2019; 14(4): e0211400.
  17. D’Argenio V et al. Clinica Chimica Acta. 2015; 446: 221-225.
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