A global study of women with inherited mutations in BRCA1 or BRCA2 found that tamoxifen could halve the risk for breast cancer in the contralateral (opposite-side) breast in these high-risk women.

Tamoxifen has been used for decades to treat breast cancer and has recently been shown to prevent breast cancers in many women. Until now, there has been limited information about whether it reduces breast cancer risk for women who are at the very highest level of risk with BRCA1 or BRCA2.

This study, led by the University of Melbourne and the Peter MacCallum Cancer Centre in Australia, involved about 2,500 women from Europe, North America, and Australia who have inherited mutations in BRCA1 or BRCA2 and who have been diagnosed with breast cancer since 1970. About one-third of these women were placed on tamoxifen.

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Tamoxifen was taken by 24% of the 1,583 BRCA1 and by 52% of the BRCA2 mutation carriers after their first breast cancer diagnosis. Over 20,104 person-years of observation, 520 contralateral breast cancers occurred. The statistical analysis of 657 BRCA1 and 426 BRCA2 mutation carriers with 100 contralateral breast cancers found an adjusted hazard ratio estimate of 0.58 for BRCA1 carriers and 0.48 for BRCA2 carriers. This study was published in the Journal of Clinical Oncology (2013; doi:10.1200/JCO.2012.47.8313).  

“In the past, the only way of reducing breast cancer risk for these high-risk women was to do invasive surgery to remove their breasts and/or ovaries. For women who choose not to undergo such surgery, or who would prefer to delay surgery until they are older, tamoxifen could now be a viable alternative,” said the lead author, Kelly-Anne Phillips, MD, of the Peter MacCallum Cancer Centre. Her previous research had found that only one in five Australian women with a mutation in BRCA1 or BRCA2 chose to undergo bilateral mastectomy to prevent cancer.

Co-author John Hopper, PhD, of the University of Melbourne, said, “In light of our findings, it is clear that women who have a mutation in BRCA1 or BRCA2 should review their management plan with their specialist and re-discuss the options available to them to lower that risk.”