Fulvestrant, a new treatment option for advanced breast cancer: tolerability versus existing agents

Owing to its favourable tolerability profile versus cytotoxic chemotherapy, endocrine therapy is the treatment of choice for postmenopausal women with hormone receptor-positive advanced breast cancer (ABC). However, tolerability concerns associated with some endocrine treatments and the potential for cross-resistance has helped to drive the need for new, effective and better-tolerated agents. Fulvestrant is a new type of oestrogen receptor antagonist with no agonist effects. In phase III trials, fulvestrant has been shown to be at least as effective as the third-generation aromatase inhibitor (AI) anastrozole in the treatment of postmenopausal women with ABC progressing on prior tamoxifen therapy. Fulvestrant is administered as a once-monthly 250 mg intramuscular injection into the gluteus muscle. Here we review the tolerability of fulvestrant in the treatment of postmenopausal women with hormone-sensitive ABC and compare it with that of the four most frequently prescribed endocrine treatments for advanced disease (tamoxifen, anastrozole, letrozole and exemestane). Compared with these agents, fulvestrant is well tolerated and is associated with a lower incidence of joint disorders compared with the non-steroidal AIs and none of the potential androgenic side-effects that are sometimes seen with steroidal AIs. It is also associated with hot flushes compared with tamoxifen. Fulvestrant therefore provides clinicians and patients with a useful, well-tolerated option for the treatment of hormone-sensitive ABC. Integration of such agents into the endocrine treatment sequence may extend the opportunity for using well-tolerated therapies before chemotherapy needs to be considered and thus may improve quality of life for patients with ABC. The overall safety profiles of newer agents such as fulvestrant will become increasingly clear with their ongoing use.