The BRCA1 gene – the first gene associated with hereditary breast cancer – was identified and cloned (isolated) in 1994 by Mark Skolnick and his colleagues in Salt Lake City, Utah. A year later the same group cloned a second breast cancer gene, BRCA2.
This milestone demonstrated that these two genes are associated with an increased risk of breast and ovarian cancer, and genetic testing for BRCA1 and BRCA2 mutations has since become an important part of medical practice.
What are BRCA mutations?
Everyone has BRCA1 and BRCA2 genes. They belong to a class of genes called tumour suppressors – they suppress the development of cancer. All cells contain DNA: a “genetic blueprint” or set of operating instructions. This DNA can become damaged, and if this happens, BRCA1 and BRCA2 are involved in repairing it. In some people however, their BRCA1 or BRCA2 gene is mutated, or faulty, and so DNA repair is significantly impaired. When cells can’t repair their DNA they may become cancerous.
How common are BRCA mutations?
Inherited mutations in BRCA genes occur at a frequency of about 1 in 250 women. They are associated with an increased risk of breast and ovarian cancer. The lifetime risk of breast cancer in a woman with either a BRCA1 or BRCA2 mutation is 60-70%. BRCA mutations account for approximately 5–10% of breast cancers and 15% of ovarian cancers. They are also associated with other cancers such as prostate, pancreatic and stomach cancer.
Preventing cancer in women with BRCA mutations
Because BRCA mutations are relatively rare, genetic screening is only recommended for individuals whose family history suggests that a mutation may be present. If testing reveals that a woman has a BRCA mutation, she has several options. She might commence earlier and more frequent cancer screening. Alternately she may choose to undergo a preventative mastectomy and/or an oophorectomy (removal of her ovaries). Both procedures have been shown to greatly reduce the risk of cancer.
Research is underway to find drug treatments that will prevent the development of BRCA-associated cancer, thus making preventative surgery unnecessary.
Treating BRCA-mutated cancers
For women with BRCA mutations who do develop cancer, understanding the effects of these mutations on cancer cells is helping doctors choose more effective treatments. For instance, there are some chemotherapy drugs that act by causing DNA damage. Because cancer cells with BRCA mutations are unable to repair DNA damage, they are likely to be especially sensitive to such drugs. Several studies have shown that a DNA-damaging drug called cisplatin is highly effective in treating BRCA-mutated breast cancer. Novel therapies are also being investigated that specifically target BRCA-mutated cancer cells.
The discovery of BRCA mutations in inherited breast and ovarian cancer is providing certainty to women with a family history of these cancers, and is enabling the development of tailored and targeted treatments.
Narod, S.A. and Foulkes, W.D. (2004). BRCA1 and BRCA2: 1994 and Beyond. Nature Reviews Cancer, 4, 665–676.
World Cancer Report 2014. Edited by Bernard W. Stewart and Christopher P. Wild. International Agency for Research on Cancer (World Health Organisation).
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