Table 1.

Prospective Studies on AS

Institution (trial no.)	Country	Year	No. of participants	Tumor size Included, cm	Primary outcome	Reference (protocol)
Asia
Kuma Hospital	Japan	1993–2019 (ongoing)	3,222 AS 2,424 IS	≤1		[11,12,14-24]
Cancer Institute Hospital	Japan	1995–2016 (ongoing)	421 AS 377 IS	≤2		[25]
Seoul National University Hospital, Seoul National University Bundang Hospital, National Cancer Center (MAeSTro) (NCT02938702)	Korea	2016–2019	755 AS 422 IS	≤1	Tumor size change LN or distant metastasis	[27-33] (Protocol [26])
Asan Medical Center, Seoul National University Bundang Hospital, Seoul St. Mary’s Hospital, and eight other hospitals (KoMPASS) (KCT0004935)	Korea	2019–ongoing	Recruiting	≤1	Progression-free survival	(Protocol [34])
North America
Memorial Sloan Kettering Cancer Center	US	NA	291 AS (no IS)	≤1.5	Tumor diameter or volume change	[10]
Cedars-Sinai Medical Center (NCT02609685)	US	2014–2021	112 AS 110 IS	≤2.0	Disease progression (tumor growth, LN, or distant metastasis)	[35]
University Health Network (NCT03271892) → Pan-Canadian (Canadian Thyroid Cancer Active Surveillance Study Group) (NCT04624477)	Canada	2016–ongoing	155 AS 45 IS→Recruiting	<2.0	Freqeuncy of patients choosing AS or surgery	[38] (Protocol [36,37])
South America
Head and Neck Cancer Center in Medellin	Colombia	2015–	102 AS (no IS)	<1.5		[39]
Santa Casa de Belo Horizonte	Brazil	2016–2019	77 AS 18 IS	≤1.2		[40]
University of Buenos Aires	Argentina		34 AS (no IS)	≤1.5		[41]
Europe
University Hospital of Pisa (NCT04129281)	Italy	2014–2020	127 AS (no IS)	≤1.3		[42,43]

AS, active surveillance; IS, immediate surgery; MAeSTro, Multicenter Prospective Cohort Study of Active Surveillance on Papillary Thyroid Microcarcinoma; LN, lymph node; KoMPASS, Korean Multicenter Prospective Cohort Study of Active Surveillance or Surgery.