Anastrozole is the standard first-line endocrine treatment for patients with hormonal receptor positive advanced breast cancer. It has been proven that the addition of fulvestrant 250mg can enhance PFS of anastrozole monotherapy according to SWOG0226 study. However, the optimal recommended dose of fulvestrant for patients with advanced breast cancer is 500mg worldwide according to CONFIRM study. The investigator designed this research to investigate whether high dose fulvestrant can further improve efficacy of anastrozole monotherapy.