Table 3.
Multivariable adjusted odds ratio (OR) and 95% confidence interval (CI) for ER/PR/HER2-defined subtypes of breast cancer associated with reproductive factors by race
| White women | African-American women | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 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 | 793 | 167 | 1.00 | 631 | 1.00 | 499 | 122 | 1.00 | 189 | 1.00 |
| 13 | 433 | 102 | 1.12 (0.84–1.48) | 327 | 0.90 (0.74–1.08) | 201 | 56 | 1.09 (0.75–1.58) | 92 | 1.18 (0.86–1.61) |
| ≥14 | 323 | 74 | 0.99 (0.72–1.36) | 220 | 0.78 (0.63–0.97) | 199 | 33 | 0.69 (0.44–1.06) | 58 | 0.75 (0.53–1.08) |
| Trend P value | 0.89 | 0.02 | 0.16 | 0.26 | ||||||
| P value for homogeneity of trends | 0.10 | 0.68 | ||||||||
| Number of completed pregnancies | ||||||||||
| Never pregnant | 199 | 56 | 1.00 | 200 | 1.00 | 51 | 12 | 1.00 | 24 | 1.00 |
| Any completed pregnancies | 1213 | 246 | 0.87 (0.61–1.24) | 822 | 0.77 (0.61–0.97) | 777 | 185 | 1.18 (0.59–2.36) | 282 | 0.89 (0.51–1.54) |
| 1 | 240 | 58 | 0.91 (0.59–1.40) | 199 | 0.86 (0.65–1.16) | 159 | 40 | 1.14 (0.54–2.43) | 78 | 1.09 (0.60–1.97) |
| 2 | 468 | 112 | 0.99 (0.67–1.45) | 358 | 0.82 (0.63–1.06) | 241 | 56 | 1.12 (0.54–2.35) | 80 | 0.79 (0.44–1.42) |
| ≥3 | 505 | 76 | 0.69 (0.45–1.05) | 265 | 0.60 (0.45–0.79) | 377 | 89 | 1.24 (0.60–2.57) | 124 | 0.76 (0.43–1.36) |
| Trend P value | 0.11 | 0.0005 | 0.62 | 0.13 | ||||||
| P value for homogeneity of trends | 0.48 | 0.12 | ||||||||
| Only non-completed pregnancy | 137 | 41 | 1.02(0.63–1.64) | 156 | 1.08 (0.78–1.49) | 71 | 14 | 0.86 (0.35–2.08) | 33 | 0.97 (0.49–1.90) |
| Parous women onlya,b | ||||||||||
| Age at first completed pregnancy, years | ||||||||||
| ≤20 | 338 | 60 | 1.00 | 162 | 1.00 | 461 | 105 | 1.00 | 135 | 1.00 |
| 21–24 | 347 | 66 | 1.03 (0.68–1.56) | 199 | 1.09 (0.82–1.44) | 163 | 41 | 1.01 (0.65–1.58) | 75 | 1.40 (0.96–2.04) |
| 25–29 | 257 | 64 | 1.09 (0.69–1.70) | 227 | 1.55 (1.14–2.10) | 91 | 21 | 1.05 (0.59–1.89) | 48 | 1.75 (1.10–2.80) |
| ≥30 | 271 | 55 | 0.70 (0.42–1.17) | 232 | 1.13 (0.80–1.60) | 62 | 18 | 1.21 (0.61–2.41) | 24 | 0.95 (0.51–1.77) |
| Trend P value | 0.21 | 0.10 | 0.62 | 0.24 | ||||||
| P value for homogeneity of trends | 0.02 | 0.66 | ||||||||
| Duration of breastfeeding, months | ||||||||||
| Never | 368 | 66 | 1.00 | 228 | 1.00 | 380 | 100 | 1.00 | 142 | 1.00 |
| Ever | 845 | 179 | 0.97 (0.68–1.38) | 592 | 0.81 (0.64–1.02) | 397 | 85 | 0.67 (0.47–0.96) | 140 | 0.78 (0.57–1.06) |
| < 6 | 343 | 84 | 1.14 (0.78–1.68) | 230 | 0.85 (0.66–1.10) | 198 | 50 | 0.79 (0.52–1.19) | 73 | 0.82 (0.57–1.18) |
| 6–11 | 194 | 29 | 0.62 (0.37–1.05) | 134 | 0.75 (0.54–1.02) | 69 | 11 | 0.54 (0.26–1.09) | 31 | 1.06 (0.63–1.77) |
| ≥ 12 | 308 | 66 | 0.88 (0.56–1.39) | 228 | 0.77 (0.57–1.04) | 130 | 24 | 0.55 (0.32–0.94) | 36 | 0.57 (0.36–0.90) |
| Trend P value | 0.27 | 0.07 | 0.01 | 0.04 | ||||||
| P value for homogeneity of trends | 0.94 | 0.47 | ||||||||
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), 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), a variable combining menopausal status and hormone therapy use (premenopausal; postmenopausal: never used hormone therapy, ever used hormone therapy; unknown menopausal status), lifetime recreational physical activity (inactive, ≤2.2, 2.3–6.6, 6.7–15.1, ≥15.2 annual metabolic equivalents of energy expenditure, 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). aModels additionally included age at first completed pregnancy (≤20, 21–24, 25–29, ≥30 years) and duration of breastfeeding (never, <6, 6–11, ≥12 months). bAdditionally, three white parous cases who had missing information on breastfeeding were excluded