Table 2.
Subgroup analysis of association between breastfeeding and childhood leukemia risk for the comparison of breastfeeding versus non/occasional breastfeeding
| 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 |
Abbreviations: PC-CS population-based case-control study; HC-CS hospital-based case-control study; NA not applicable
1One study was conducted in the United States, Canada and Australia