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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