1073 Background: Endocrine therapy is a key modality in the management of estrogen receptor positive metastatic breast cancer. Fulvestrant (ICI 182,780) is an estrogen receptor downregulator. It has previously been shown to be as effective as anastrozole in patients who had previously progressed on tamoxifen. Methods: A retrospective study was carried out of metastatic breast cancer patients treated at Charing Cross Hospital between 2002–2005 who had received fulvestrant following treatment failure with tamoxifen and a third generation aromatase inhibitor. All patients were postmenopausal and received fulvestrant 250mg IM every 28 days. Measurable disease was assessed by response evaluation criteria in solid tumors (RECIST). Results: A total of 45 patients were identified with a median age of 60 (range 36 to 90). The ER status was known in 95% (n=43) of patients and was positive in all cases, it was unknown in 2% (n=2). At the time of commencing fulvestrant, 96% (n=43) had metastatic disease and 4% (n=2) locally advanced disease. All patients had received at least 2 lines of prior endocrine therapy (including adjuvant therapy), at time of starting fulvestrant the median number of prior regimens was 3 (range 3–5). Fulvestrant was administered for a median of 4 months (range 1 to 20 months), with 4 patients currently still receiving therapy as of 1 November 2006. Of the 45 patients, 2.2% (n=1) achieved a partial response, while 31% (n=14) achieved stable disease for at least 6 months. Thus, 33.3% (n=15) obtained clinical benefit (defined as PR or SD for at least 6 months). The response rates based on line of therapy will be presented. Of the 45 patients, 41 were evaluable for survival data. The median survival of the remaining patients from the start of fulvestrant therapy was 9 months (range 1 to 48 months). Of the 44 patients, 14% (n=6) remain alive. The treatment was well tolerated and toxicity data will be presented. Conclusions: Fulvestrant is well tolerated and is efficacious as treatment for advanced breast cancer that has failed tamoxifen and a third generation aromatase inhibitors. No significant financial relationships to disclose.