Table 3.
Multivariate-adjusted1 HRs (95% CI) for birth index and time between menarche and first birth in relation to breast cancer subtypes in the Nurses' Health Studies
| Luminal A | Luminal B | HER2-enriched | Basal-like | Unclassified | All Subtypes | |
|---|---|---|---|---|---|---|
| N, cases | 1572 | 771 | 163 | 284 | 78 | 2868 |
| Time between menarche and first birth | ||||||
| 22-year increase2 | 1.40 (1.13, 1.74) | 0.82 (0.60, 1.12) | 2.84 (1.38, 5.86) | 1.80 (1.08 3.00) | 2.57 (1.01, 6.57) | 1.32 (1.12, 1.55) |
| P heterogeneity | 0.003 | |||||
| Birth index | ||||||
| 102-unit increase3 | 0.93 (0.77, 1.13) | 0.79 (0.60, 1.03) | 1.59 (0.86, 2.96) | 1.50 (0.95, 2.39) | 0.79 (0.32, 1.92) | 0.95 (0.83, 1.10) |
| P heterogeneity | 0.50 | |||||
| Duration of premenopause | ||||||
| 1-year increase | 1.10 (1.09, 1.12) | 1.08 (1.06, 1.09) | 1.08 (1.04, 1.13) | 1.04 (1.01, 1.07) | 1.09 (1.03, 1.15) | 1.09 (1.08, 1.10) |
| P heterogeneity | 0.06 | |||||
| Duration of menopause | ||||||
| 1-year increase | 1.05 (1.04, 1.06) | 1.02 (1.01, 1.03) | 1.04 (1.02, 1.07) | 1.02 (0.99, 1.04) | 0.97 (0.92, 1.02) | 1.03 (1.03, 1.04) |
| P heterogeneity | 0.01 | |||||
1
Mutually adjusted for all variables in table + breastfeeding, 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