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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

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

  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  
  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), 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