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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

From: Reproductive factors and the risk of triple-negative breast cancer in white women and African-American women: a pooled analysis

  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       
  1. 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 + 
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