Table 2.
Multivariable adjusted odds ratio (OR) and 95% confidence interval (CI) for ER/PR/HER2-defined subtypes of breast cancer associated with reproductive factors
| Controls | Triple-negative | Luminal A-like | Luminal B-like | HER2-enriched | |||||
|---|---|---|---|---|---|---|---|---|---|
| N | N | OR (95% CI) | N | OR (95% CI) | N | OR (95% CI) | N | OR (95% CI) | |
| All women | |||||||||
| Age at menarche, years | |||||||||
| ≤ 12 | 1292 | 289 | 1.00 | 820 | 1.00 | 186 | 1.00 | 110 | 1.00 |
| 13 | 634 | 158 | 1.13 (0.90–1.41) | 419 | 0.98 (0.84–1.16) | 99 | 1.06 (0.81–1.40) | 66 | 1.22 (0.88–1.69) |
| ≥ 14 | 522 | 107 | 0.89 (0.69–1.14) | 278 | 0.77 (0.64–0.92) | 75 | 0.92 (0.68–1.24) | 51 | 1.07 (0.75–1.53) |
| Trend P value | 0.55 | 0.009 | 0.70 | 0.56 | |||||
| P value for homogeneity of trends | 0.19 | ||||||||
| Number of completed pregnancies | |||||||||
| Never pregnant | 250 | 68 | 1.00 | 224 | 1.00 | 56 | 1.00 | 31 | 1.00 |
| Any completed pregnancies | 1990 | 431 | 0.91 (0.67–1.24) | 1104 | 0.79 (0.64–0.98) | 263 | 0.82 (0.58–1.15) | 176 | 0.78 (0.50–1.20) |
| 1 | 399 | 98 | 0.95 (0.66–1.36) | 277 | 0.92 (0.71–1.19) | 84 | 1.17 (0.79–1.74) | 50 | 1.02 (0.62–1.67) |
| 2 | 709 | 168 | 0.98 (0.70–1.37) | 438 | 0.81 (0.64–1.02) | 109 | 0.88 (0.61–1.29) | 59 | 0.69 (0.42–1.11) |
| ≥3 | 882 | 165 | 0.84 (0.60–1.19) | 389 | 0.64 (0.50–0.81) | 70 | 0.53 (0.35–0.80) | 67 | 0.65 (0.40–1.05) |
| Trend P value | 0.26 | <0.0001 | <0.0001 | 0.02 | |||||
| P value for homogeneity of trends | 0.09 | ||||||||
| Only non-completed pregnancy | 208 | 55 | 0.91 (0.60–1.38) | 189 | 1.02 (0.76–1.35) | 41 | 0.88 (0.55–1.39) | 20 | 0.69 (0.38–1.26) |
| Parous women onlya,b | |||||||||
| Age at first completed pregnancy, years | |||||||||
| ≤20 | 799 | 165 | 1.00 | 297 | 1.00 | 69 | 1.00 | 62 | 1.00 |
| 21–24 | 510 | 107 | 1.03 (0.78–1.38) | 274 | 1.22 (0.98–1.52) | 63 | 1.18 (0.80–1.73) | 43 | 1.05 (0.68–1.62) |
| 25–29 | 348 | 85 | 1.08 (0.77–1.52) | 275 | 1.64 (1.28–2.10) | 56 | 1.22 (0.78–1.89) | 33 | 1.10 (0.66–1.85) |
| ≥30 | 333 | 73 | 0.80 (0.54–1.20) | 256 | 1.17 (0.88–1.55) | 75 | 1.09 (0.68–1.74) | 38 | 0.96 (0.55–1.70) |
| Trend P value | 0.50 | 0.05 | 0.57 | 0.95 | |||||
| P value for homogeneity of trends | 0.24 | ||||||||
| Duration of breastfeeding, months | |||||||||
| Never | 748 | 166 | 1.00 | 370 | 1.00 | 81 | 1.00 | 60 | 1.00 |
| Ever | 1242 | 264 | 0.80 (0.63–1.02) | 732 | 0.78 (0.65–0.94) | 182 | 0.89 (0.65–1.23) | 116 | 0.91 (0.63–1.32) |
| < 6 | 541 | 134 | 0.96 (0.74–1.26) | 303 | 0.83 (0.68–1.02) | 82 | 0.99 (0.70–1.41) | 35 | 0.68 (0.43–1.07) |
| 6–11 | 263 | 40 | 0.55 (0.37–0.82) | 165 | 0.76 (0.59–0.99) | 35 | 0.70 (0.44–1.12) | 33 | 1.28 (0.78–2.09) |
| ≥ 12 | 438 | 90 | 0.69 (0.50–0.96) | 264 | 0.71 (0.56–0.90) | 65 | 0.85 (0.56–1.30) | 48 | 1.10 (0.69–1.75) |
| Trend P value | 0.006 | 0.004 | 0.28 | 0.36 | |||||
| P value for homogeneity of trends | 0.08 | ||||||||
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, African-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), 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 seven parous case participants who had missing information on breastfeeding were excluded. Triple negative = estrogen receptor (ER)–/progesterone receptor (PR)–/human epidermal growth factor receptor-2 (HER2)–, Luminal A-like = ER+ and/or PR+ plus HER2–, Luminal B-like = ER+ and/or PR+ plus HER2+, HER2-enriched = ER–/PR– /HER2 +