You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Introduction<br />
Breast cancer evolution and progression is deeply influenced by both estrogen receptor<br />
(<strong>ER</strong>) and growth factor receptor signaling. In recent years, the field of cancer therapy has<br />
witnessed the emergence of multiple targeted strategies that inhibit specific key<br />
molecules and pathways important for tumor growth and progression. Among them,<br />
endocrine therapy to block <strong>ER</strong> activity and signaling, the first targeted therapy in<br />
oncology, is still the most successful systemic therapy in the management of <strong>ER</strong>-positive<br />
breast cancer.<br />
Tamoxifen, which binds to and antagonizes <strong>ER</strong> has been the mainstay of endocrine<br />
(hormonal) therapy in both early and advanced breast cancer patients for almost three<br />
decades (1, 2). Recently its role has also expanded to preventive therapy in patients at<br />
high risk of developing the disease (3). Unfortunately, however, approximately 50% of<br />
patients with advanced disease do not respond to first line treatment with the selective<br />
estrogen receptor modulator (S<strong>ER</strong>M) tamoxifen (de novo or upfront, intrinsic resistance).<br />
Furthermore, almost all patients with metastatic disease and many that receive tamoxifen<br />
as adjuvant therapy eventually experience tumor relapse and die from their disease<br />
(acquired resistance). Thus, de novo and acquired resistance to tamoxifen occur<br />
frequently in breast cancer patients and seriously limit the efficacy of this treatment.<br />
3
Change language