Nearly one-fifth of breast tumors have extra copies of the gene encoding one form of the estrogen receptor ESR1, suggests a study published online this week in Nature Genetics.
A small-scale initial study shows that women treated with tamoxifen, which blocks the activity of the estrogen receptor, survive longer if their tumor has this gene amplification.
Estrogen receptor expression is one of the most important known factors in the development of breast cancer, and assessing its status is important for determining the use of anti-estrogen receptor therapies like tamoxifen.
Ronald Simon and colleagues examined more than 2,000 breast cancer samples for evidence of amplification of ESR1, and detected it in nearly two-thirds of the tumors. In a small follow-up study of 175 women with breast cancer who were being treated with tamoxifen, they found that women with the amplification survived longer than those who did not, even though the tumors in both groups of women expressed ESR1. The authors suggest that ESR1 amplification may identify a subgroup of breast cancers that would be particularly likely to respond to anti-estrogen therapy.