Table 4.
Multivariate-adjusted1 HRs (95% CI) for birth index and time between menarche and first birth by history of breastfeeding (ever/never) in relation to breast cancer subtypes in the Nurses' Health Studies
| Luminal A | Luminal B | HER2-enriched | Basal | Unclassified | All Subtypes | |
|---|---|---|---|---|---|---|
| N, cases | 1419 | 684 | 143 | 254 | 61 | 2561 |
| Time between menarche and first birth | ||||||
| Never breastfed | ||||||
| 22-year increase2 | 1.66 (1.25, 2.22) | 0.93 (0.59, 1.45) | 3.51 (1.40, 8.82) | 2.49 (1.27, 4.89) | 1.83 (0.46, 7.34) | 1.56 (1.26, 1.94) |
| P heterogeneity | 0.07 | |||||
| Ever breastfed | ||||||
| 22-year increase2 | 1.09 (0.85, 1.41) | 0.80 (0.56, 1.16) | 1.66 (0.67, 4.13) | 1.22 (0.66, 2.25) | 1.76 (0.51, 6.10) | 1.04 (0.86, 1.26) |
| P heterogeneity | 0.59 | |||||
| Pdifference (never v. ever breastfed) | 0.001 | 0.46 | 0.04 | 0.03 | 0.97 | <0.0001 |
| Birth index | ||||||
| Never breastfed | ||||||
| 102-unit increase3 | 0.83 (0.63, 1.10) | 0.74 (0.50, 1.10) | 0.96 (0.38, 2.45) | 1.67 (0.90, 3.12) | 0.61 (0.15, 2.42) | 0.85 (0.69, 1.04) |
| P heterogeneity | 0.24 | |||||
| Ever breastfed | ||||||
| 102-unit increase3 | 0.86 (0.69, 1.08) | 0.80 (0.59, 1.10) | 1.45 (0.70, 2.99) | 1.24 (0.71, 2.17) | 0.40 (0.11, 1.41) | 0.88 (0.75, 1.04) |
| P heterogeneity | 0.35 | |||||
| Pdifference (never v. ever breastfed) | 0.22 | 0.54 | 0.12 | 0.82 | 0.57 | 0.10 |
1
Mutually adjusted for all variables in table + HT use, BMI at 18, weight change since 18, history of BBD, family history of breast cancer, total physical activity, alcohol intake, height, cohort
2
22 years: uniparous (age at menarche = 13 years, age first birth = 35 years) vs. nulliparous
3
102 units: multiparous (4 births at ages 20, 23, 26 and 29 years) vs. nulliparous; age at menarche 13 years