Table 2. Hazard Ratios of Childhood Cancer Associated With Exclusive Breastfeeding Duration by Childhood Cancer Groups and Diagnoses.
| Cancer type, breastfeeding duration | Person-years | Events, No. | Crude model | Adjusted modela | ||
|---|---|---|---|---|---|---|
| HR (95% CI) | P valueb | Adjusted HR (95% CI) | P valueb | |||
| Any cancer | ||||||
| Total | 1 679 635 | 332 | NA | NA | NA | NA |
| Exclusive breastfeeding duration | ||||||
| Never or <14 d | 191 314 | 45 | 1 [Reference] | .30 | 1 [Reference] | .23 |
| ≤2 mo | 367 242 | 82 | 0.95 (0.67-1.38) | 0.97 (0.68-1.41) | ||
| 3-5 mo | 792 367 | 143 | 0.77 (0.56-1.09) | 0.76 (0.55-1.08) | ||
| ≥6 mo | 328 713 | 62 | 0.82 (0.56-1.20) | 0.79 (0.54-1.18) | ||
| Linear trend per 1-mo increasec | 1 488 321 | 287 | 0.98 (0.93-1.03) | .48 | 0.98 (0.92-1.03) | .34 |
| Exclusive breastfeeding duration, mo | ||||||
| 0-2 | 558 556 | 127 | 1 [Reference] | .06 | 1 [Reference] | .04 |
| ≥3 | 1 121 079 | 205 | 0.81 (0.65-1.01) | 0.79 (0.63-0.99) | ||
| Hematologic cancers | ||||||
| Total | NA | 124 | NA | NA | NA | NA |
| Exclusive breastfeeding duration | ||||||
| Never or <14 d | 191 390 | 15 | 1 [Reference] | .20 | 1 [Reference] | .13 |
| ≤2 mo | 367 376 | 37 | 1.30 (0.73-2.43) | 1.31 (0.73-2.46) | ||
| 3-5 mo | 792 649 | 51 | 0.83 (0.48-1.53) | 0.79 (0.45-1.47) | ||
| ≥6 mo | 328 853 | 21 | 0.83 (0.43-1.64) | 0.78 (0.40-1.55) | ||
| Linear trend per 1-mo increasec | 1 488 879 | 109 | 0.92 (0.84-1.00) | .055 | 0.91 (0.83-0.99) | .04 |
| Exclusive breastfeeding duration, mo | ||||||
| 0-2 | 558 767 | 52 | 1 [Reference] | .04 | 1 [Reference] | .03 |
| ≥3 | 1 121 502 | 72 | 0.70 (0.49-0.99) | 0.66 (0.46-0.95) | ||
| ALL | ||||||
| Total | NA | 81 | NA | NA | NA | NA |
| Exclusive breastfeeding duration | ||||||
| Never or <14 d | 191 402 | 9 | 1 [Reference] | .31 | 1 [Reference] | .24 |
| ≤2 mo | 367 402 | 25 | 1.48 (0.72-3.35) | 1.50 (0.73-3.41) | ||
| 3-5 mo | 792 724 | 34 | 0.94 (0.47-2.09) | 0.92 (0.45-2.04) | ||
| ≥6 mo | 328 875 | 13 | 0.87 (0.37-2.10) | 0.82 (0.35-2.01) | ||
| Linear trend per 1-mo increasec | 1 489 001 | 72 | 0.93 (0.83-1.03) | .15 | 0.92 (0.82-1.02) | .12 |
| Exclusive breastfeeding duration, mo | ||||||
| 0-2 | 558 804 | 34 | 1 [Reference] | .12 | 1 [Reference] | .09 |
| ≥3 | 1 121 599 | 47 | 0.70 (0.45-1.10) | 0.67 (0.43-1.06) | ||
| BCP-ALL | ||||||
| Total | NA | 74 | NA | NA | NA | NA |
| Exclusive breastfeeding duration | ||||||
| Never or <14 d | 191 402 | 8 | 1 [Reference] | .23 | 1 [Reference] | .14 |
| ≤2 mo | 367 407 | 24 | 1.60 (0.75-3.81) | 1.63 (0.76-3.90) | ||
| 3-5 mo | 792 742 | 30 | 0.94 (0.45-2.20) | 0.89 (0.42-2.09) | ||
| ≥6 mo | 328 877 | 12 | 0.91 (0.38-2.31) | 0.83 (0.34-2.14) | ||
| Linear trend per 1-mo increasec | 1 489 026 | 66 | 0.91 (0.82-1.02) | .10 | 0.90 (0.80-1.01) | .07 |
| Exclusive breastfeeding duration, mo | ||||||
| 0-2 | 558 809 | 32 | 1 [Reference] | .09 | 1 [Reference] | .04 |
| ≥3 | 1 121 619 | 42 | 0.67 (0.42-1.07) | 0.62 (0.39-0.99) | ||
| CNS tumors | ||||||
| Total | NA | 44 | NA | NA | NA | NA |
| Exclusive breastfeeding duration, mo | ||||||
| 0-2 | 558 907 | 15 | 1 [Reference] | .93 | 1 [Reference] | .91 |
| ≥3 | 1 121 678 | 29 | 0.97 (0.53-1.86) | 0.96 (0.51-1.88) | ||
| Linear trend per 1-mo increasec | 1 489 155 | 39 | 1.03 (0.89-1.17) | .72 | 1.03 (0.89-1.18) | .67 |
| Solid tumors | ||||||
| Total | NA | 80 | NA | NA | NA | NA |
| Exclusive breastfeeding duration, mo | ||||||
| 0-2 | 558 854 | 29 | 1 [Reference] | .60 | 1 [Reference] | .58 |
| ≥3 | 1 121 565 | 51 | 0.88 (0.56-1.41) | 0.87 (0.55-1.41) | ||
| Linear trend per 1-mo increasec | 1 489 027 | 66 | 1.02 (0.92-1.13) | .73 | 1.01 (0.90-1.12) | .88 |
| Neuroblastoma | ||||||
| Total | NA | 14 | NA | NA | NA | NA |
| Exclusive breastfeeding duration, mo | ||||||
| 0-2 | 558 926 | 5 | 1 [Reference] | .89 | 1 [Reference] | .98 |
| ≥3 | 1 121 716 | 9 | 0.92 (0.32-3.00) | 0.98 (0.32-3.06) | ||
| Linear trend per 1-mo increasec | 1 489 213 | <14d | 1.04 (0.81-1.30) | .73 | 1.05 (0.83-1.34) | .66 |
Abbreviations: ALL, acute lymphoblastic leukemia; BCP, B-cell precursor; CNS, central nervous system; HR, hazard ratio; NA, not applicable.
Adjusted for year of birth (linearly), birth weight (linearly, in 1-g intervals), gestational age (linearly, in 1-day intervals), mother’s age at delivery (linearly, in 1-year intervals), mode of birth (vaginal or cesarean delivery), and mother’s highest educational level and stratified by sex and birth order.
P values and 95% CIs were based on the likelihood ratio.
Children exclusively breastfed for less than 14 days or never were excluded.
Exact number is not presented to blind numbers less than 5 (directly or by calculation through group totals), in accordance with the interpretation of the General Data Protection Regulation by Statistics Denmark.