Table 3.

Assessment of the risk of bias in retrospective studies using the modified Newcastle–Ottawa scale.

	Selection			Comparability		Outcome
	Assignment for treatment#	Representative treatment group	Representative reference group	Comparable for 1, 2, and 3*	Comparable for 4, 5, 6, 7, and 8*	Assessment of outcome	Adequate follow-up	Quality score
Huang 2015	No	Yes	Yes	1, 2, 3	4, 5, 6, 7, 8	Yes	Yes	★★★★★★★★
Xie 2019	No	Yes	Yes	1, 3	4, 5, 6, 7, 8	Yes	No	★★★★★★

Comparability variables: 1 = age; 2 = Eastern Cooperative Oncology Group; 3 = Menopausal status ; 4 = Tumor stage; 5 = Clinical nodal stage; 6 = Estrogen receptor/progesterone receptor status; 7 = human epidermal growth factor receptor 2 status; 8 = Ki67 index. *: Two stars, all characteristics were comparable; one star, two or three characteristics were comparable; no star, zero or one characteristic was comparable. #: Details of the criteria for the adequate random assignment of patients to treatments were provided.