Hideaki Kanemura
Over 70% of women with breast cancer are with hormone receptor positive disease [1], and most of them are treated
with an adjuvant endocrine therapy. Five years tamoxifen used to be a standard adjuvant endocrine treatment of breast
cancer. It was shown by a metaanalysis that tamoxifen reduced about 40% of recurrence rates in both premenopausal
and postmenopausal women with breast cancer [2]. Third generation Aromatase Inhibitors (AIs), exemestane (steroidal),
anastrozole (non-steroidal), and letrozole (non-steroidal) began to be used in late 90’s as an adjuvant endocrine therapy in
postmenopausal women with breast cancer. A randomized controlled trial showed that 5 years adjuvant anastrozole was
superior to 5 years adjuvant tamoxifen in terms of disease-free survival (DFS) rates [3]. In addition another randomized
controlled trial showed that 5 years of adjuvant letrozole was superior to 5 years adjuvant tamoxifen in terms of DFS
rates and overall survival (OS) rates [4].
