Table 1. Characteristics of included studies.

Reference	Study period	Country	Tumor type	Data Sources	Sample size	Stage	Method	Analysis	Outcome	data	NOS
Wu et al[17]	1999–2008	China	DA	Institutional	141	I-IV	CR	UV	OS	indirect	9
Schwameis et al[18]	1994–2012	Austria	SBA	Institutional	26	NR	CR	UV	OS	indirect	6
Guo et al[19]	2000–2011	China	SBA	Institutional	149	NR	CR	UV	OS	indirect	8
Young et al[20]	1992–2010	United States	SBA	National	1644	I-IV	CR	MU	OS	direct	9
Kanhan et al[21]	1996–2011	Britain	SBA	Institutional	48	ES	CR	UV	OS/RFS	direct	8
Ecker et al[22]	1998–2011	United States	SBA	National	2297	I-IV	CR	UV	OS	direct	8
Legue et al[23]	1999–2013	Netherlands	SBA	National	1194	I-IV	CR	MU	OS	direct	8
Fu et al[24]	1997–2009	United States	DA	Institutional	64	III	CRT	MU	OS/DFS	direct	7
Aydin et al[25]	2003–2013	Turkey	SBA	Institutional	78	I-IV	CR	UV	OS/DFS	direct	9
Kim et al[26]	1991–2002	Korea	DA	Institutional	24	I-IV	CRT	UV	OS/RFS	indirect	8
Koo et al[27]	1989–2009	Korea	SBA	Institutional	52	I-IV	CR	MU	OS/DFS	direct	7
Overman et al[28]	1990–2006	United States	SBA	Institutional	54	I-IV	CRT	MU	OS/DFS	direct	8
Poultsides et al[29]	1984–2006	United States	DA	Institutional	122	I-IV	CRT	MU	OS	direct	9
Zaanan et al[30]	1996–2008	France	SBA	Institutional	93	NR	CR	UV	OS/RFS	direct	9
Ecker et al[31]	1998–2011	United States	DA	National	256	NR	CR	UV	OS	direct	9

SBA: small bowel adenocarcinoma; DA: duodenal adenocarcinoma; NR: not reported; ES: Early stage; CR: Chemotherapy; CRT: Chemoradiation; UV: univariate; MU: multivariate; OS: overall survival; RFS: recurrence-free survival; DFS: disease-free survival; NOS: Newcastle-Ottawa Scale. NOS: Newcastle-Ottawa Scale.