Table 2 The independent prognostic factors by multivariable Cox regression with the backward stepwise selection method in the training cohort

Age

1.03

1.03-1.04

< 0.0001

Grade

 Well

1

-

-

 Moderately

1.84

1.12-3.02

0.016

 Poorly

3.19

1.99-5.12

< 0.0001

 Undifferentiated

3.15

1.97-5.03

< 0.0001

Ethnic group

 White

1

-

-

 Black

1.21

1.01-1.46

0.043

 Other

0.85

0.69-1.06

0.146

Marital status

 Married

1

-

-

 Single

1.29

1.12-1.49

0.0004

 SDW²

1.22

1.1-1.36

0.0002

Insurance

 Yes

1

-

-

 No

1.39

1.09-1.76

0.007

AJCC

 I

1

-

-

 II

3.59

3.17-4.07

< 0.0001

 III

6.8

5.74-8.07

< 0.0001

 IV

18.04

15.6-20.86

< 0.0001

Size

 1-20 mm

1

-

-

 21-49 mm

1.19

1.03-1.37

0.021

 ≥ 50 mm

1.52

1.31-1.75

< 0.0001

Regional lymph nodes removed

 Yes

1

-

-

 No

1.99

1.76-2.24

< 0.0001

Chemotherapy

 Yes

1

-

-

 No

1.41

1.27-1.56

< 0.0001