Understanding the biologic mechanisms responsible for breast-cancer progression during tamoxifen or fulvestrant treatment

"Resurrection of clinical efficacy" after resistance to endocrine therapy in metastatic breast cancer

“…However, with acquired resistance, he noted that the intra-tumoral concentration of tamoxifen was substantially reduced at relapse, despite no change in plasma levels. Hardin et al [ 8 ] demonstrated that dehydroepiandrosterone sulphate (DHEAS) exposure, even in the presence of tamoxifen and fulvestrant, induced changes in ER and PgR gene expression that may be partially responsible for breast cancer progression.…”