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References:
Phillips K-A, Milne RL, Rookus MA et al. Tamoxifen and risk of contralateral breast cancer for BRCA1 and BRCA2 mutation carriers. Journal of Clinical Oncology. 2013;31:3091-3099.

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For BRCA Mutation Carriers, Tamoxifen Reduces Risk of Cancer
in Opposite Breast

Date of publication: September 1, 2013

Among women with a history of breast cancer and a BRCA1 or BRCA2 gene mutation, preventive treatment with tamoxifen may reduce the risk of cancer in the opposite breast, even if the first breast cancer was estrogen receptor-negative. These results were published in the Journal of Clinical Oncology.

Inherited mutations in two genes—BRCA1 and BRCA2—have been found to greatly increase the lifetime risk of developing breast and ovarian cancer. Mutations in these genes can be passed down through either the mother's or the father's side of the family.

Tamoxifen is a type of hormonal therapy known as a selective estrogen-receptor modulator. It is used in the treatment of hormone receptor-positive breast cancer, and is also used to reduce the likelihood of breast cancer in women who are at high risk of the disease. The role of tamoxifen in breast cancer prevention among women with a BRCA1 or BRCA2 mutation, however, has been uncertain.

To evaluate preventive use of tamoxifen among women with a BRCA1 or BRCA2 mutation, researchers combined information from three previous studies. The analysis focused on women with one of these gene mutations and a history of breast cancer. The goal was to determine if tamoxifen reduced the likelihood of cancer in the opposite breast. Tamoxifen was used by 24% of the women with a BRCA1 mutation and 52% of the women with a BRCA2 mutation.

  • Tamoxifen reduced the risk of cancer in the opposite breast by more than half among both BRCA1 and BRCA2 mutation carriers.
  • Although information about the estrogen receptor status of the initial breast cancer was available for only a subset of the women, the benefit of tamoxifen on the opposite breast did not appear to vary by this characteristic. In other words, tamoxifen reduced the risk of cancer in the opposite breast even if the original breast cancer was estrogen receptor-negative.
  • A limitation of this study is that it relied on observational data, and was not a randomized clinical trial. Observational studies can be prone to certain types of bias.
Although not definitive, this study suggests that tamoxifen reduces the risk of cancer in the opposite breast among BRCA1 or BRCA2 mutation carriers who have a history of breast cancer. This benefit of tamoxifen did not appear to vary by the estrogen receptor status of the initial breast cancer.

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