The purpose of this study is to compare the efficacy of Faslodex (fulvestrant) to Nolvadex (tamoxifen) as first-line treatment for postmenopausal women with advanced breast cancer. Patients will be treated until disease progression or until the investigator has determined that treatment is not in the best interest of the patient, whichever occurs first.

Inclusion Criteria:

• Biopsy confirmation of breast cancer. Evidence of breast cancer that is not considered amenable to curative treatment.

Postmenopausal women. Written informed consent to participate in the study.

Exclusion Criteria:

• Previous treatment with hormonal therapy unless that therapy was tamoxifen for adjuvant breast cancer. The use of tamoxifen must have ceased at least one year before this study.

Previous treatment with Faslodex. Any existing serious disease, illness, or condition that will prevent participation or compliance with the study procedures.

Treatment with an investigational or non-approved drug within one month of then start of the study.