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Table 4 Breastfeeding and breast cancer risk by ER/PR status

From: Reproductive factors and breast cancer risk according to joint estrogen and progesterone receptor status: a meta-analysis of epidemiological studies

Study Subgroups by MP status Exposure categories (n) Highest/Lowest exposure category RR (95% CI) for highest vs. lowest category
     ER+PR+ ER-PR-
Population-based case-control studies
[11] All women 2 Ever/Never 0.7 (0.5–1.0) 0.8 (0.5–1.1)
  Pre-MP 2 Ever/Never 0.7 (0.4–1.1) 0.7 (0.4–1.1)
  Post-MP 2 Ever/Never 0.8 (0.5–1.2) 1.1 (0.6–1.8)
[12] Young 3 >12 months/Never 0.80 (0.58–1.12) 0.75 (0.50–1.12)
[13] All women 3 >6 months/Never or nulliparous 1.05 (0.79–1.39) 1.01 (0.69–1.48)
  Pre-MP 3 >6 months/Never or nulliparous 1.41 (0.96–2.08) 0.86 (0.53–1.39)
  Post-MP 3 >6 months/Never or nulliparous 0.92 (0.73–1.16) 1.09 (0.77–1.52)
[7] All women 4 >6 months/Never 0.76 (0.65–0.89) 0.68 (0.55–0.83)
[8] Young 4 >6 months/Never 0.51 (0.31–0.84) 0.57 (0.33–1.00)
Summary RRs for population-based case-control studies 0.78 (0.64–0.94) 0.74 (0.61–0.89)
P for homogeneity between ER+PR+ and ER-PR- cancer p = 0.80
Hospital-based case-control studies
[15] All women Per 3 months↑ 3 months' increase 1.02 (0.95–1.09) 0.98 (0.90–1.07)
[16] 40–80 3 ≥12 months/Never 1.25 (0.67–2.50) 0.91 (0.48–1.67)
Summary RRs for hospital-based case-control studies 1.02 (0.92–1.14) 0.98 (0.88–1.09)
Summary RRs by MP status Pre-MP/Young    0.83 (0.61–1.14) 0.73 (0.53–1.00)
  Post-MP    0.89 (0.62–1.27) 1.09 (0.77–1.56)
Summary RRs for all studies 0.95 (0.87–1.05) 0.91 (0.83–1.00)
P for homogeneity between ER+PR+ and ER-PR- cancer p = 0.38
  1. Test for homogeneity across all studies: P ER+PR+= 0.15 and P ER-PR- = 0.17. Egger's test for publication bias for all studies: P ER+PR+ = 0.18 and P ER-PR- = 0.18. CI, confidence interval; ER+, estrogen receptor-positive; ER-, estrogen receptor-negative; ER/PR, estrogen and progesterone receptor; MP, menopausal or menopause; Per 3 months↑, Per 3 months' increase in the duration of breastfeeding; PR+, progesterone receptor-positive; PR-, progesterone receptor-negative; RR, relative risk.