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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

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

  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  
  1. 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