Metastatic breast cancer: sequencing hormonal therapy and positioning of fulvestrant.

Fulvestrant, a novel estrogen receptor (ER) antagonist with no agonist effects, binds, blocks, and degrades the ER, thereby downregulating cellular ER levels, which in turn leads to reduced expression of the progesterone receptor. Due to this specific working mechanism, fulvestrant is an important addition to the armamentarium of endocrine agents in advanced breast cancer (ABC). Fulvestrant has been shown to be equally effective as the third-generation aromatase inhibitor (AI) anastrozole in postmenopausal patients with hormone-sensitive ABC progressing prior to tamoxifen. In another randomized phase III trial, it was shown that fulvestrant had similar efficacy to tamoxifen in the first-line treatment of postmenopausal women with hormone receptor-positive ABC. When comparing the side effects of fulvestrant with tamoxifen and anastrozole, it was shown that fulvestrant is well tolerated compared with these agents and is associated with a lower incidence of joint disorders. Clinical benefit on fulvestrant treatment after AI therapy has been reported in a substantial number of patients (28-46%). On the other hand, it was also shown that sensitivity to further endocrine therapy is retained following progression on first-line or second-line fulvestrant (57% and 46% clinical benefit, respectively). In conclusion, fulvestrant provides us with an additional endocrine treatment option making it possible to prolong the time that patients with ABC can be treated with endocrine therapy.