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Table 5 Multivariable adjusted odds ratio (OR) and 95% confidence interval (CI) for ER/PR/HER2-defined subtypes of breast cancer associated with duration of breastfeeding among parous women by race and age

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)
Younger (20–44 years)a
 Duration of breastfeeding, months
  Never 85 27 1.00 57 1.00 119 37 1.00 43 1.00
  Ever 383 105 0.85 (0.49–1.49) 218 0.71 (0.46–1.11) 148 37 0.43 (0.22–0.83) 48 0.58 (0.32–1.06)
   <6 136 43 0.94 (0.52–1.72) 72 0.70 (0.43–1.14) 73 26 0.67 (0.33–1.36) 25 0.64 (0.32–1.26)
   ≥6 247 62 0.76 (0.41–1.41) 146 0.73 (0.45–1.18) 75 11 0.18 (0.07–0.46) 23 0.50 (0.24–1.06)
  Trend P value    0.34   0.28    0.0004   0.07
   P value for homogeneity of trends 0.93      0.09  
Older (45–64 years)b
 Duration of breastfeeding, months
  Never 283 39 1.00 171 1.00 261 63 1.00 96 1.00
  Ever 462 74 1.06 (0.65–1.72) 374 0.83 (0.63–1.10) 249 48 0.74 (0.47–1.17) 92 0.90 (0.62–1.30)
    < 6 207 41 1.30 (0.78–2.19) 158 0.91 (0.67–1.25) 125 24 0.69 (0.39–1.21) 48 0.94 (0.60–1.46)
    ≥ 6 255 33 0.75 (0.41–1.38) 216 0.73 (0.53–1.02) 124 24 0.81 (0.46–1.43) 44 0.85 (0.54–1.35)
  Trend P value    0.41   0.07    0.35   0.49
   P value for homogeneity of trends 0.85      0.72  
  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 Women’s BCIS Study, 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), 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 (1, 2, ≥3), oral contraceptive use (never, <1, 1–4, 5–9, ≥10 years) and age at first completed pregnancy (≤20, 21–24, 25–29, ≥30 years). aAdditionally three white younger case participants who had missing information on breastfeeding were excluded. bAdditionally adjusted for a variable combining menopausal status and hormone therapy use (premenopausal; postmenopausal: never used hormone therapy, ever used hormone therapy; unknown menopausal status)