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Fulvestrant Comparable to Tamoxifen in Women with Hormone Receptor-Positive Breast Cancers

Fulvestrant appears to be comparable to tamoxifen and the 2 therapies may also be similarly effective in a subgroup of women with hormone receptor-positive breast cancers, a new study suggests.

Fulvestrant (Faslodex; AstraZeneca Pharmaceuticals LP, Wilmington, DE) is the first of a new type of oestrogen receptor (ER) antagonist that downregulates the ER. In contrast to tamoxifen, fulvestrant appears to be devoid of partial agonist properties.

Anthony Howell, MD, with the Christie Hospital and Holt Radium Institute, in Manchester, United Kingdom and colleagues evaluated the efficacy and tolerability of fulvestrant for the treatment of advanced breast cancer in postmenopausal women.

Patients with metastatic/locally advanced breast cancer previously untreated for advanced disease were randomised to receive either fulvestrant, 250 mg, via intramuscular injection, once monthly (n = 313) or tamoxifen 20 mg, orally, once daily (n = 274).


All tumours were positive for ER (ER+) and/or progesterone receptor (PgR+), or had an unknown receptor status.

After a median follow-up of 14.5 months, both treatment groups were similar in terms of time to progression (TTP; median TTP, 6.8 months and 8.3 months, respectively; hazard ratio, 1.18; 95% CI, 0.98 to 1.44; P = .088).

Furthermore, approximately 78% of the patients had known ER+ and/or PgR+ tumours. In these patients, median TTP was 8.2 months for fulvestrant and 8.3 months for tamoxifen (hazard ratio, 1.10; 95% CI, 0.89 to 1.36; P =.39).

According to the researchers, the overall objective response rate was 31.6% with fulvestrant and 33.9% with tamoxifen whereas in the known hormone receptor-positive subgroup, objective response rate was 33.2% and 31.1%, respectively.

Both treatments were well tolerated. A total of 129 patients in the fulvestrant group (41.6%) and 139 patients in the tamoxifen group (51.3%) experienced drug-related adverse events. The most frequent drug-related adverse events were vasodilatation, injection-site pain, and nausea for both treatments.

"Since these drugs work by different mechanisms and are not cross-resistant, they can be used in conjunction with all other endocrine therapies to provide lengthy disease control before more toxic chemotherapy is initiated," Dr. Howell and colleagues conclude.

Further clinical trials are planned to investigate whether use of a loading regimen of fulvestrant may further improve efficacy. An additional first-line trial of fulvestrant versus anastrozole is also planned, they note.



J Clin Oncol 2004;22:1605-13. "Comparison of fulvestrant versus tamoxifen for the treatment of advanced breast cancer in postmenopausal women previously untreated with endocrine therapy: a multinational, double-blind, randomized trial"

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