Table 2
A summary of research studies on adjuvant aromatase inhibitor

Study	Design	Subject	Treatment	Results
IBCSG	Randomized	4,922 Patients	Letrozole × 5 yr vs.	For letrozole:
BIG 1-98, 2007 [65]	Phase III	ER (+)	Tamoxifen × 5 yr	Recurrence 18%↓
	Double-blind	Postmenopausal
		Early breast cancer
		51-mo follow-up
IBCSG	Randomized	6,182 Patients	Letrozole × 5 yr vs.	For switching:
BIG 1-98, 2009 [28]	Phase III	ER (+)	Tamoxifen × 5 yr vs.	Not more effective
	Double-blind	Postmenopausal	Letrozole × 2 yr	Letrozole vs. tamoxifen:
		Early breast cancer	→tamoxifen × 3 yr vs.	No difference in mortality
		71-mo follow-up	Tamoxifen × 2 yr
			→letrozole × 3 yr
ATAC, 2010 [26]	Randomized	5,216 Patients	Anastrozole × 5 yr vs.	For anastrozole × 5 yr:
		Postmenopausal	Tamoxifen × 5 yr vs.	Recurrence 14% ↓
		Early breast cancer	Anastrozole+tamoxifen × 5 yr	No difference in mortality
		ER/PR (+)
		120-mo follow-up
EBCTCG, 2010 [12]	Meta-analysis	9,856 Patients	AI × 5 yr vs.	For AI × 5 yr:
		5.8-yr follow-up	Tamoxifen × 5 yr	Recurrence 2.9% ↓
		9,015 Patients	Tamoxifen × 2–3 yr	For switching:
		3.9-yr follow-up	→tamoxifen vs.	Recurrence 3.1% ↓
		after switching	Tamoxifen×2–3 y	Breast cancer mortality 0.7% ↓
			→AI
MA.17, 2012 [29]	Randomized	5,170 Patients	Tamoxifen × 5 yr	For adding AI × 5 yr:
	Double-blind	Postmenopausal	→AI for 5 yr vs.	Disease free survival ↑(HR, 0.58)
	Phase III	ER/PR (+)	Tamoxifen ×5 yr	Overall survival ↑(HR, 0.76)
		64-yr follow-up	→placebo ×5 yr

IBCSG, International Breast Cancer Study Group; BIG, Breast International Group; ER, estrogen receptor; ATAC, arimidex, tamoxifen, alone or in combination; PR, progesterone receptor; EBCTCG, Early Breast Cancer Trialists’ Collaborative Group; AI, aromatase inhibitor.