Table 2.
Relationship between reproductive factors and risk of invasive breast cancer by subtype
| Risk factor | Controls (n = 941)
|
ER+ cases (n = 781)
|
Triple-negative (n = 184)
|
HER2-overexpressing cases (n = 60)
|
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| n | % | n | % | OR* | 95 % CI | n | % | OR* | 95 % CI | n | % | OR* | 95 % CI | |
| Age at menarche (years) | ||||||||||||||
| <12 | 191 | 20.3 | 171 | 21.9 | 1.0 | Ref | 44 | 23.9 | 1.0 | Ref | 11 | 18.3 | 1.0 | Ref |
| 12–13 | 523 | 55.6 | 441 | 56.5 | 0.9 | 0.7–1.2 | 102 | 55.4 | 0.8 | 0.6–1.3 | 42 | 70.0 | 1.4 | 0.7–2.7 |
| ≥14 | 227 | 24.1 | 169 | 21.6 | 0.8 | 0.6–1.1 | 38 | 20.7 | 0.7 | 0.5–1.2 | 7 | 11.7 | 0.5 | 0.2–1.4 |
| P value for trend: | 0.219 | 0.199 | 0.221 | |||||||||||
| P value versus ER + cases: 0.594 | P value versus ER+ cases: 0.441 | |||||||||||||
| Parity (ever had a live birth) | ||||||||||||||
| Nulliparous | 188 | 20.0 | 207 | 26.5 | 1.0 | Ref | 51 | 27.7 | 1.0 | Ref | 11 | 18.3 | 1.0 | Ref |
| Parous | 753 | 80.0 | 574 | 73.5 | 0.7 | 0.5–0.8† | 133 | 72.3 | 0.7 | 0.5–1.0† | 49 | 81.7 | 1.1 R+ | 0.6–2.2 |
| P value versus ER + cases: 0.960 | P value versus ER+ cases: 0.110 | |||||||||||||
| Number of live births (parous women only) | ||||||||||||||
| 1 | 192 | 25.5 | 161 | 28.0 | 1.0 | Ref | 33 | 24.8 | 1.0 | Ref | 14 | 28.6 | 1.0 | Ref |
| 2 | 363 | 48.2 | 282 | 49.1 | 0.9 | 0.7–1.1 | 68 | 51.1 | 1.0 | 0.6–1.6 | 23 | 46.9 | 0.8 | 0.4–1.6 |
| ≥3 | 198 | 26.3 | 131 | 22.8 | 0.7 | 0.5–0.9† | 32 | 24.1 | 0.7 | 0.4–1.2 | 12 | 24.5 | 0.6 | 0.2–1.4 |
| P value for trend: | 0.015 | 0.172 | 0.220 | |||||||||||
| P value versus ER + cases: 0.425 | P value versus ER+ cases: 0.779 | |||||||||||||
| Age at first live birth, years (parous women only) | ||||||||||||||
| <20 | 59 | 7.8 | 56 | 9.8 | 1.4 | 0.9–2.2 | 21 | 15.8 | 1.6 | 0.9–3.1 | 5 | 10.2 | 1.2 | 0.4–3.5 |
| 20–24 | 162 | 21.5 | 117 | 20.4 | 1.0 | Ref | 37 | 27.8 | 1.0 | Ref | 12 | 24.5 | 1.0 | Ref |
| 25–29 | 228 | 30.3 | 188 | 32.8 | 1.1 | 0.8–1.5 | 35 | 26.3 | 0.6 | 0.4–1.0 | 20 | 40.8 | 1.1 | 0.5–2.4 |
| 30–34 | 204 | 27.1 | 143 | 24.9 | 0.8 | 0.6–1.2 | 30 | 22.6 | 0.5 | 0.3–0.9† | 8 | 16.3 | 0.5 | 0.2–1.2 |
| ≥35 | 100 | 13.3 | 70 | 12.2 | 0.7 | 0.5–1.1 | 10 | 7.5 | 0.4 | 0.2–0.8† | 4 | 8.2 | 0.4 | 0.1–1.5 |
| Per 5 years | 0.94 | 0.85–1.03 | 0.77 | 0.65–0.91 | 0.85 | 0.65–1.10 | ||||||||
| P value for trend: | 0.201 | 0.001 | 0.210 | |||||||||||
| P value versus ER + cases: 0.020 | P value versus R+ cases: 0.230 | |||||||||||||
| Interval between age at menarche and age at first live birth, years (parous women only) | ||||||||||||||
| <10 | 141 | 18.7 | 109 | 19.0 | 1.0 | Ref | 40 | 30.1 | 1.0 | Ref | 14 | 28.6 | 1.0 | Ref |
| 10–14 | 200 | 26.6 | 163 | 28.4 | 1.0 | 0.7–1.4 | 36 | 27.1 | 0.6 | 0.4–1.0 | 8 | 16.3 | 0.4 | 0.2–1.0† |
| 15–19 | 237 | 31.5 | 157 | 27.4 | 0.8 | 0.5–1.1 | 29 | 21.8 | 0.4 | 0.2–0.6† | 17 | 34.7 | 0.7 | 0.3–1.5 |
| >20 | 175 | 23.2 | 145 | 25.3 | 0.9 | 0.6–1.2 | 28 | 21.1 | 0.5 | 0.3–0.9† | 10 | 20.4 | 0.5 | 0.2–1.4 |
| P value for trend: | 0.102 | 0.006 | 0.114 | |||||||||||
| P value versus ER + cases: 0.051 | P value versus ER+ cases: 0.337 | |||||||||||||
| Age at most recent live birth, years (parous women only) | ||||||||||||||
| <25 | 79 | 10.5 | 62 | 10.8 | 1.0 | Ref | 23 | 17.3 | 1.0 | Ref | 6 | 12.2 | 1.0 | Ref |
| 25–29 | 151 | 20.1 | 132 | 23.0 | 1.2 | 0.8–2.0 | 30 | 22.6 | 0.9 | 0.5–1.9 | 14 | 28.6 | 1.5 | 0.4–4.8 |
| 30–34 | 282 | 37.5 | 207 | 36.2 | 1.1 | 0.7–2.0 | 56 | 42.1 | 1.2 | 0.5–2.6 | 18 | 36.7 | 1.5 | 0.4–5.7 |
| ≥35 | 241 | 32.0 | 173 | 30.1 | 1.2 | 0.7–2.3 | 24 | 18.0 | 0.6 | 0.2–1.7 | 11 | 22.4 | 1.6 | 0.3–8.0 |
| P value for trend: | 0.679 | 0.516 | 0.701 | |||||||||||
| P value versus ER+ cases: 0.378 | P value versus ER+ cases: 0.822 | |||||||||||||
| Time since last live birth (years) (parous women only) | ||||||||||||||
| <5 | 265 | 35.2 | 161 | 28.0 | 1.0 | Ref | 41 | 30.8 | 1.0 | Ref | 16 | 32.7 | 1.0 | Ref |
| 5–9.9 | 243 | 32.3 | 182 | 31.7 | 1.2 | 0.9–1.6 | 41 | 30.8 | 1.1 | 0.6–1.8 | 12 | 24.5 | 0.8 | 0.3–1.8 |
| ≥10 | 245 | 32.5 | 231 | 40.2 | 1.5 | 1.0–2.2 | 51 | 38.3 | 1.0 | 0.5–2.0 | 21 | 42.9 | 1.2 | 0.5–3.4 |
| P value for trend: | 0.062 | 0.884 | 0.712 | |||||||||||
| P value versus ER+ cases: 0.338 | P value versus ER+ cases 0.735 | |||||||||||||
| Breastfeeding (parous women only) | ||||||||||||||
| Never | 60 | 8.0 | 53 | 9.3 | 1.0 | Ref | 19 | 14.3 | 1.0 | Ref | 4 | 8.2 | 1.0 | Ref |
| Ever | 692 | 92.0 | 519 | 90.7 | 0.9 | 0.6–1.4 | 114 | 85.7 | 0.6 | 0.4–1.1 | 45 | 91.8 | 1.2 | 0.4–3.9 |
| <6 months | 190 | 25.3 | 143 | 25.0 | 0.9 | 0.6–1.4 | 45 | 33.8 | 0.9 | 0.5–1.6 | 14 | 28.6 | 1.2 | 0.4–3.9 |
| 6–11 months | 111 | 14.8 | 93 | 16.3 | 1.1 | 0.7–1.7 | 17 | 12.8 | 0.6 | 0.3–1.2 | 9 | 18.4 | 1.5 | 0.4–5.4 |
| >12 months | 389 | 51.9 | 283 | 49.5 | 1.0 | 0.6–1.5 | 52 | 39.1 | 0.5 | 0.3–0.9† | 22 | 44.9 | 1.1 | 0.3–3.6 |
| P value for trend: | 0.606 | 0.018 | 0.086 | |||||||||||
| P value versus ER+ cases: 0.009 | P value versus ER+ cases: 0.713 | |||||||||||||
*
All odds ratios (OR) are adjusted for 5-year age group and reference year. Number of live births is additionally adjusted for age at first live birth, the interval between age at menarche and age at first live birth is additionally adjusted for number of live births, and age at most recent live birth, time since last live birth, and breastfeeding history is additionally adjusted for age at first live birth and number of live births
†
P value <0.05