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Table 2 Parity 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)
     ER+PR+ ER-PR-
Cohort studies
[9] Post-MP 3 ≥3/Nulliparous 0.75 (0.52–1.06) 2.24 (0.69–7.24)
    Per birth 0.96 (0.89–1.03) 1.09 (0.91–1.30)
[10] All women 3 4/Nulliparous 0.74 (0.61–0.89) 1.17 (0.80–1.70)
    Per birth 0.88 (0.79–0.98) 1.13 (0.92–1.41)
Summary RRs for cohort studies Highest/Nulliparous 0.74 (0.50–1.10) 1.25 (0.84–1.87)
    Per birth 0.93 (0.80–1.08) 1.11 (0.95–1.29)
Population-based case-control studies
[12] Young 2 Ever/Nulliparous 0.83 (0.60–1.15) 0.82 (0.55–1.23)
    Per birth 0.91 (0.77–1.07) 0.91 (0.74–1.11)
[13] All women 4 ≥3/Nulliparous 0.62 (0.43–0.90) 0.77 (0.46–1.27)
    Per birth 0.90 (0.82–0.97) 0.94 (0.84–1.06)
  Pre-MP 4 ≥3/Nulliparous 0.44 (0.26–0.75) 0.90 (0.46–1.76)
    Per birth 0.83 (0.73–0.94) 0.97 (0.83–1.14)
  Post-MP 4 ≥3/Nulliparous 0.71 (0.53–0.97) 0.72 (0.46–1.12)
    Per birth 0.92 (0.86–0.98) 0.93 (0.84–1.03)
[14] Young 4 ≥3/Nulliparous 1.0 (0.5–1.2) 0.8 (0.4–1.3)
    Per birth 1.00 (0.90–1.11) 0.94 (0.81–1.09)
[7] All women 4 ≥3/Nulliparous 0.63 (0.54–0.73) 1.07 (0.86–1.32)
    Per birth 0.86 (0.82–0.90) 1.01 (0.95–1.08)
[8] Young 4 ≥3/Nulliparous 0.61 (0.42–0.88) 0.93 (0.60–1.44)
    Per birth 0.86 (0.78–0.95) 0.95 (0.84, 1.06)
Summary RRs for population-based case-control studies Highest/Nulliparous 0.67 (0.55–0.82) 0.96 (0.79–1.17)
    Per birth 0.88 (0.83–0.94) 0.98 (0.92–1.04)
Hospital-based case-control study
[15]   Per birth Per birth 0.96 (0.79–1.17) 1.00 (0.81–1.23)
Summary RRs by MP status Pre-MP/Young   Highest/Nulliparous 0.72 (0.52–0.98) 0.86 (0.63–1.18)
    Per birth 0.90 (0.82–0.98) 0.95(0.86–1.04)
  Post-MP   Highest/Nulliparous 0.72 (0.44–1.17) 0.86 (0.53–1.42)
    Per birth 0.93 (0.84–1.03) 0.97 (0.88–1.08)
Summary RRs for all studies Highest/Nulliparous 0.75 (0.65–0.88) 1.01 (0.87–1.17)
    Per birth 0.89 (0.84–0.94) 0.99 (0.94–1.05)
P for homogeneity between ER+PR+ and ER-PR- cancer Highest/Nulliparous p <0.001
    Per birth p <0.001
  1. Test for homogeneity across all studies: P ER+PR+ = 0.52 and P ER-PR- = 0.77 for highest/nulliparous, P ER+PR+ = 0.84 and P ER-PR-= 0.80 per birth. Egger's test for publication bias for all studies: P ER+PR+ = 0.98 and P ER-PR- = 0.87. CI, confidence interval; ER+, estrogen receptor-positive; ER-, estrogen receptor-negative; ER/PR, estrogen and progesterone receptor; MP, menopausal or menopause; PR+, progesterone receptor-positive; PR-, progesterone receptor-negative; RR, relative risk.