Table 3.
Multivariable-adjusteda hazard ratios (HRs) and 95% confidence intervals for molecular breast cancer subtypes in relation to parity and breastfeeding: Nurses’ Health Study (1976–2012) and Nurses’ Health Study II (1989–2013)
| Luminal A | Luminal B | HER2-enriched | Basal-like | Phet by subtype | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cases | PY | HR (95%CI) | Cases | PY | HR (95%CI) | Cases | PY | HR (95%CI) | Cases | PY | HR (95%CI) | ||
| Parity/breastfeeding | |||||||||||||
| Nulliparous | 199 | 743,688 | 1 (ref.) | 109 | 743,762 | 1 (ref.) | 9 | 743,854 | 1 (ref.) | 34 | 743,835 | 1 (ref.) | |
| Parous women, never breastfed | 613 | 1,361,275 | 1.00 (0.85–1.18) | 269 | 1,361,572 | 0.82 (0.65–1.04) | 62 | 1,361,777 | 2.09 (1.02–4.30) | 121 | 1,361,712 | 1.34 (0.90–2.00) | 0.04b |
| 1 child | 89 | 210,499 | 1.07 (0.83–1.38) | 48 | 210,527 | 1.11 (0.78–1.56) | 13 | 210,562 | 3.35 (1.41–7.93) | 14 | 210,562 | 1.08 (0.58–2.03) | 0.03c |
| 2 children | 228 | 517,884 | 1.05 (0.87–1.28) | 92 | 518,005 | 0.78 (0.58–1.03) | 29 | 518,065 | 2.81 (1.31–6.05) | 45 | 518,050 | 1.40 (0.89–2.22) | |
| ≥ 3 children | 296 | 632,891 | 0.93 (0.77–1.12) | 129 | 633,040 | 0.76 (0.58–1.00) | 20 | 633,150 | 1.29 (0.57–2.90) | 62 | 633,100 | 1.43 (0.92–2.23) | |
| Parous women, ever breastfed | 1091 | 3,187,450 | 0.87 (0.74–1.01) | 556 | 3,187,935 | 0.80 (0.65–0.99) | 115 | 3,188,338 | 1.90 (0.95–3.80) | 186 | 3,188,280 | 0.96 (0.66–1.40) | |
| 1 child | 92 | 314,469 | 0.98 (0.76–1.26) | 51 | 314,504 | 0.97 (0.70–1.36) | 9 | 314,536 | 1.94 (0.77–4.92) | 16 | 314,532 | 0.99 (0.54–1.80) | |
| 2 children | 340 | 1,168,513 | 0.87 (0.73–1.03) | 174 | 1,168,664 | 0.77 (0.61–0.99) | 26 | 1,168,794 | 1.43 (0.66–3.09) | 55 | 1,168,780 | 0.84 (0.54–1.30) | |
| ≥ 3 children | 659 | 1,704,468 | 0.84 (0.71–0.99) | 331 | 1,704,767 | 0.78 (0.62–0.98) | 80 | 1,705,008 | 2.11 (1.03–4.29) | 115 | 1,704,968 | 1.05 (0.70–1.57) | |
aAdjusted for age, height (< 1.60, 1.60 to < 1.65, 1.65 to < 1.70, 1.70 to < 1.75, 1.75+ meters), BMI at age 18 (< 20, 20–21.9, 22–23.9, 24–26.9, 27+ kg/m2), weight change since age 18 (continuous, kg), age at menarche (< 12, 12, 13, 14, 15+ years), menopausal status (premenopausal, postmenopausal or unknown), age at natural menopause (continuous), HT use (never, past, current E only, current E + P, current other), alcohol consumption (non-drinker, < 5, 5–10, 10–15, 15+ g/day), total physical activity (< 3, 3–9, 9–18, 18–27, 27+ MET-h/day), family history of breast cancer (yes/no), history of benign breast disease (yes/no), age at first birth (continuous, years)
bPhet for nulliparous and parous ever vs. never breastfed
cPhet for nulliparous and number of children by ever vs. never breastfed