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Risk in Women with Abnormal BRCA1 Gene Linked to Other Abnormal Genes

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Most inherited cases of breast cancer are associated with two abnormal genes: BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two). Women with an abnormal BRCA1 or BRCA2 gene have up to an 85% risk of developing breast cancer by age 70. Their risk of ovarian cancer also is higher than average.

A study found that women with an abnormal BRCA1 gene who had been diagnosed with breast cancer tended to have one or more of five other abnormal genes -- called single nucleotide polymorphisms (SNPs). Women with an abnormal BRCA1 gene who hadn't been diagnosed with breast cancer didn't tend to have one or more of the five abnormal SNPs. All the abnormal SNPs were located on chromosome 19. None of the abnormal SNPs were linked to an increase in ovarian cancer risk in women with an abnormal BRCA1 gene.

This research is a genome study. In the future, genome testing for these five abnormal SNPs might help doctors more precisely determine breast cancer risk in women who have an abnormal BRCA1 gene.

The researchers also looked to see if two of the five abnormal SNPs were linked to breast cancer risk in women with an abnormal BRCA2 gene; there was no link.

The researchers also looked to see if the five abnormal SNPs were linked to breast cancer risk in women who didn't have an abnormal BRCA1 or BRCA2 gene. They found:

  • The five abnormal SNPs were linked to a slightly lower risk of hormone-receptor-negative breast cancer and a slightly higher risk of hormone-receptor-positive breast cancer.
  • Some of the five abnormal SNPs were linked to a higher risk of triple-negative breast cancer and others were linked to a lower risk. Triple-negative breast cancer is breast cancer that is estrogen-receptor-negative, progesterone-receptor-negative and HER2-negative.

Women with an abnormal breast cancer gene have a number of options to reduce the risk of developing breast cancer, as well as ways to detect any cancer that develops earlier, when it's most treatable, including:

  • a more aggressive screening plan, starting at an earlier age
  • hormonal therapy to block the effect of estrogen on breast tissue or reduce the amount of estrogen in the body
  • removing the healthy breasts (prophylactic mastectomy)

Some women with an abnormal BRCA1 or BRCA2 gene also may consider having their healthy ovaries removed because of the increase in ovarian cancer risk. Removing the ovaries also dramatically lowers estrogen levels and lower estrogen levels can reduce the risk of hormone-receptor-positive breast cancer.

Having a more precise way to determine breast cancer risk, such as testing for the five abnormal SNPs this research discovered, could help doctors and women with an abnormal BRCA1 gene make more informed decisions about risk reduction options.

Stay tuned to Breastcancer.org Research News to learn about the latest results that can lead to better ways to prevent, diagnose, and treat breast cancer.

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