Table 2. Baseline characteristics of the included studies.

Trial	Year	Description of trial arms	Trial population	Outcome measures	Median follow-up (years)
MA 17	2003	Phase-III placebo controlled; 5 y Letrozole vs. placebo after 5 y Tamoxifen	5,157	DFS, OS, DDFS, CBC	5.3
ABCSG 6a	2007	Phase-III open-label; 3 y Anastrozole vs. observation after 5 y Tamoxifen	856	OS, RFS, CBC	5.2
NSABP-33	2008	Phase-III placebo controlled; 5 y Exemestane vs. placebo after 5 y Tamoxifen	1,598	DFS, RFS	2.5
NSABP-42	2016	Phase-III placebo controlled; 5 y Letrozole vs. placebo after 5 y Tamoxifen ± AI	3,923	OS, DFS, DRFS, CBC	6.9
DATA	2016	Phase-III open-label; 6 y vs. 3 y Anastrozole after 5 years Tamoxifen ± AI	1,660	DFS, OS, RFS	4.1
LATER	2016	Phase-III open-label; 5 y Letrozole vs. observation after 4≥ Tamoxifen ± AI	360	RFS, OS	3.9
IDEAL	2016	Phase-III open-label; 5 y vs. 2.5 y Letrozole after initial 5 y Tamoxifen ± AI	1,824	DFS, OS, RFS	6.6
MA 17R	2016	Phase-III placebo controlled; 5 y Letrozole vs. placebo after initial 5 y Tamoxifen ± AI	1,918	OS, DFS, RFS	6.3

OS, overall survival; DFS, disease-free survival; RFS, recurrence-free survival; DRFS, distant recurrence-free survival; CBC, contralateral breast cancer; DDFS, distant disease-free survival.