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Table 2 Subgroup analysis of association between breastfeeding and childhood leukemia risk for the comparison of breastfeeding versus non/occasional breastfeeding

From: Breastfeeding and the risk of childhood cancer: a systematic review and dose-response meta-analysis

 

No. of studies

No. of cases

OR (95%CI)

P value

I2 (%)

P value for heterogeneity

P in meta-regression

Cancer type

      

0.629

 AML (A.1)

11

1241

0.96 (0.79 ~ 1.18)

0.723

38.9

< 0.001

 

 ALL (A.2)

27

11,554

0.92 (0.84 ~ 1.00)

0.057

66.4

< 0.001

0.500

 B cell ALL (A.3)

6

3974

0.91 (0.81 ~ 1.01)

0.070

47.3

0.350

 

 T cell ALL (A.4)

4

472

1.00 (0.79 ~ 1.26)

0.996

8.6

0.091

 

Year of publication

      

0.921

 In and before 2000 (A.5)

10

5018

0.76 (0.59 ~ 0.97)

0.030

84.7

< 0.001

 

 After 2000 (A.6)

23

10,135

0.77 (0.62 ~ 0.97)

0.023

94.5

< 0.001

 

Geographic location

      

0.016

 Europe (A.7)

14

7518

0.89 (0.77 ~ 1.04)

0.147

81.2

< 0.001

 

 Asia (A.8)

8

1739

0.43 (0.19 ~ 0.98)

0.044

94.1

< 0.001

 

 North America or Oceania (A.9)

11

5896

0.93 (0.79 ~ 1.09)

0.386

77.6

< 0.001

0.259

 North America only (A.10)

8

3285

1.01 (0.84 ~ 1.21)

0.960

74.0

< 0.001

 

 Oceania only (A.11)

2

411

0.63 (0.36 ~ 1.12)

0.113

29.0

0.235

 

 Both1 (A.12)

1

2200

0.79 (0.69 ~ 0.90)

< 0.001

NA

NA

 

Study quality score

      

0.280

 < 7 (A.13)

10

2752

0.97 (0.74 ~ 1.28)

0.827

70.5

< 0.001

 

 ≥ 7 (A.14)

23

12,401

0.72 (0.59 ~ 0.87)

0.001

94.7

< 0.001

 

Sample size

      

0.787

 ≤ 500 (A.15)

15

1938

0.77 (0.64 ~ 0.93)

0.007

59.3

0.002

 

 > 500 (A.16)

18

13,215

0.78 (0.61 ~ 1.01)

0.061

95.9

< 0.001

 

Study design

      

0.490

 PC-CS (A.17)

22

11,524

0.86 (0.76 ~ 0.96)

0.009

81.0

< 0.001

 

 HC-CS (A.18)

10

3451

0.61 (0.29 ~ 1.32)

0.214

96.8

< 0.001

 

 Cohort study (A.19)

1

178

1.02 (0.70 ~ 1.48)

0.917

NA

NA

 

Definition of reference category

      

0.024

 Never breastfeeding (A.20)

25

13,278

0.87 (0.72 ~ 1.04)

0.132

93.8

< 0.001

 

 Occasional breastfeeding (A.21)

8

1875

0.47 (0.28 ~ 0.80)

0.005

88.8

< 0.001

0.872

  ≤ 6 months (A.22)

5

440

0.49 (0.35 ~ 0.67)

< 0.001

21.7

0.276

 

  ≤ 1 month (A.23)

3

1435

0.50 (0.15 ~ 1.60)

0.240

95.9

< 0.001

 
  1. Abbreviations: PC-CS population-based case-control study; HC-CS hospital-based case-control study; NA not applicable
  2. 1One study was conducted in the United States, Canada and Australia