Efficacy of fulvestrant 500 mg in Japanese postmenopausal advanced/recurrent breast cancer patients and factors associated with prolonged time-to-treatment failure

<b><i>Objective</i>:</b> We aimed to confirm the efficacy of fulvestrant in Japanese postmenopausal advanced/recurrent breast cancer (ABC) patients, and investigate factors contributing to time-to-treatment failure (TTF) prolongation.<b><i>Research design and methods</i>:</b> This retrospective study included 194 ABC patients who received fulvestrant (500 mg) from January 2012 to December 2014.<b><i>Main outcome measures</i>:</b> TTF (efficacy measure), overall survival (OS), factors prolonging TTF and adverse events were evaluated.<b><i>Results</i>:</b> The median age was 65 (42 – 90) years. Overall, TTF was 5.48 months. In patients without prior chemotherapy (n = 59), OS was significantly longer (p = 0.0131) than in patients with prior chemotherapy (n = 135). There was no strong correlation between TTF with fulvestrant and other endocrine therapies, total duration of endocrine therapy and maximum duration of endocrine therapy. TTF was significantly longer in patients with less than two prior chemotherapy regimens (p = 0.0093), <i>de novo</i> metastatic disease (p = 0.0124) and without liver metastasis (p = 0.0024). We observed one case each of pulmonary infarction and psychiatric disorder.<b><i>Conclusions</i>:</b> Fulvestrant is effective for ABC patients and may show greater efficacy in patients with few prior chemotherapy regimens, <i>de novo</i> metastatic disease and absence of liver metastasis. Prior endocrine therapy duration might not be a predictive factor for fulvestrant TTF in heavily treated ABC patients.