Table 4.
Multivariable adjusted odds ratio (OR) and 95% confidence interval (CI) for ER/PR/HER2-defined subtypes of breast cancer associated with reproductive factors by age
| Younger (20–44 years) | Oldera (45–64 years) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Controls | Triple-negative | Luminal A-like | Controls | Triple-negative | Luminal A-like | |||||
| N | N | OR (95% CI) | N | OR (95% CI) | N | N | OR (95% CI) | N | OR (95% CI) | |
| All women | ||||||||||
| Age at menarche, years | ||||||||||
| ≤12 | 491 | 139 | 1.00 | 299 | 1.00 | 801 | 150 | 1.00 | 521 | 1.00 |
| 13 | 252 | 94 | 1.35 (0.98–1.85) | 152 | 0.94 (0.72–1.22) | 382 | 64 | 0.90 (0.65–1.25) | 267 | 0.94 (0.77–1.16) |
| ≥14 | 227 | 58 | 0.86 (0.60–1.23) | 98 | 0.63 (0.47–0.85) | 295 | 49 | 0.85 (0.59–1.22) | 180 | 0.85 (0.67–1.08) |
| Trend P value | 0.72 | 0.004 | 0.33 | 0.18 | ||||||
| P-value for homogeneity of trends | 0.06 | 0.92 | ||||||||
| Number of completed pregnancies | ||||||||||
| Never pregnant | 115 | 47 | 1.00 | 91 | 1.00 | 135 | 21 | 1.00 | 133 | 1.00 |
| Any completed pregnancies | 735 | 207 | 0.88 (0.58–1.32) | 368 | 0.75 (0.54–1.05) | 1255 | 224 | 1.06 (0.64–1.77) | 736 | 0.82 (0.62–1.09) |
| 1 | 193 | 48 | 0.75 (0.46–1.23) | 107 | 0.83 (0.56–1.23) | 206 | 50 | 1.30 (0.73–2.31) | 170 | 1.01 (0.72–1.42) |
| 2 | 289 | 83 | 0.94 (0.60–1.48) | 159 | 0.82 (0.57–1.19) | 420 | 85 | 1.15 (0.67–1.96) | 279 | 0.80 (0.59–1.09) |
| ≥ 3 | 253 | 76 | 0.98 (0.61–1.56) | 102 | 0.59 (0.40–0.88) | 629 | 89 | 0.85 (0.49–1.48) | 287 | 0.70 (0.51–0.96) |
| Trend P value | 0.73 | 0.02 | 0.13 | 0.006 | ||||||
| P value for homogeneity of trends | 0.03 | 0.83 | ||||||||
| Only non-completed pregnancy | 120 | 37 | 0.91 (0.54–1.53) | 90 | 1.03 (0.68–1.57) | 88 | 18 | 1.08 (0.54–2.19) | 99 | 1.10 (0.74–1.65) |
| Parous women onlyb,c | ||||||||||
| Age at first completed pregnancy, years | ||||||||||
| ≤ 20 | 235 | 71 | 1.00 | 85 | 1.00 | 564 | 94 | 1.00 | 212 | 1.00 |
| 21–24 | 142 | 43 | 1.02 (0.63–1.65) | 80 | 1.44 (0.95–2.17) | 368 | 64 | 1.05 (0.72–1.54) | 194 | 1.11 (0.85–1.44) |
| 25–29 | 168 | 50 | 0.94 (0.57–1.56) | 99 | 1.48 (0.97–2.27) | 180 | 35 | 1.20 (0.74–1.94) | 176 | 1.84 (1.34–2.51) |
| ≥30 | 190 | 42 | 0.62 (0.34–1.12) | 102 | 1.15 (0.71–1.86) | 143 | 31 | 1.08 (0.61–1.89) | 154 | 1.32 (0.91–1.90) |
| Trend P value | 0.15 | 0.52 | 0.60 | 0.01 | ||||||
| P value for homogeneity of trends | 0.07 | 0.27 | ||||||||
| Duration of breastfeeding, months | ||||||||||
| Never | 204 | 64 | 1.00 | 100 | 1.00 | 544 | 102 | 1.00 | 270 | 1.00 |
| Ever | 531 | 142 | 0.75 (0.50–1.12) | 266 | 0.70 (0.50–0.99) | 711 | 122 | 0.85 (0.62–1.17) | 466 | 0.83 (0.67–1.03) |
| < 6 | 209 | 69 | 0.93 (0.60–1.44) | 97 | 0.72 (0.49–1.05) | 332 | 65 | 0.97 (0.67–1.39) | 206 | 0.90 (0.70–1.16) |
| 6–11 | 126 | 22 | 0.49 (0.27–0.89) | 64 | 0.68 (0.44–1.07) | 137 | 18 | 0.62 (0.35–1.10) | 101 | 0.84 (0.60–1.17) |
| ≥ 12 | 196 | 51 | 0.60 (0.35–1.01) | 105 | 0.68 (0.44–1.05) | 242 | 39 | 0.79 (0.50–1.24) | 159 | 0.71 (0.53–0.96) |
| Trend P value | 0.02 | 0.12 | 0.17 | 0.03 | ||||||
| P value for homogeneity of trends | 0.32 | 0.93 | ||||||||
Triple-negative = estrogen receptor (ER)–/progesterone receptor (PR)–/human epidermal growth factor receptor-2 (HER2)–, Luminal A-like = ER+ and/or PR+ plus HER2. Models in multivariate analysis included sub-study (the Women’s CARE Study or the Women’s BCIS Study, the Women’s LIFE Study), study site (Los Angeles, Detroit), race (white, Africa-American), reference age (in 5-year age categories), education (≤ high school, technical school or some college, college graduate), first-degree breast cancer family history (no, yes), body mass index (<25, 25–29, ≥30 kg/m2), lifetime recreational physical activity (inactive, ≤2.2, 2.3–6.6, 6.7–15.1, ≥15.2 annual metabolic energy equivalents, hour/week), alcohol intake (never, former, current), cigarette smoking status (never, former, current), age at menarche (≤12,13, ≥14 years), number of completed pregnancies (never pregnant, 1, 2, ≥3, only non-completed pregnancy), oral contraceptive use (never, <1, 1–4, 5–9, ≥10 years). aAdditionally adjusted for a variable combining menopausal status and hormone therapy use (premenopausal; postmenopausal: never used hormone therapy, ever used hormone therapy; unknown menopausal status). bModels additionally included age at first completed pregnancy (≤20, 21–24, 25–29, ≥30 years) and duration of breastfeeding (never, <6, 6–11, ≥12 months). cAdditionally three younger case participants who had missing information on breastfeeding were excluded