Scientists have discovered that resistance to tamoxifen treatment can be mediated by a modification of the estrogen receptor. These results, published in the journal Cancer Cell, enhance the understanding of what underlies tamoxifen resistance in breast cancer and may eventually allow for earlier identification of resistant tumors, providing critical time to choose an alternative therapeutic strategy that is more likely to be effective.

Because nearly three-quarters of all breast cancers are stimulated by estrogen acting at functional estrogen receptors (ER+), they are most often treated with anti-estrogen compounds that inactivate the estrogen receptor. The most common of these is the drug tamoxifen. However, only about half of ER+ breast cancers successfully respond to treatment with tamoxifen, while the other half are resistant.