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Table 3 Age at first birth 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) Oldest/youngest age category RR (95% CI) for oldest vs. youngest age category
     ER+PR+ ER-PR-
Cohort study
[9] Post-MP 2 ≥30/<30 1.76 (1.21–2.56) 1.71 (0.76–3.85)
Population-based case-control studies
[11] All women 2 >25/≤ 25 1.3 (0.9–1.8) 0.8 (0.5–1.3)
  Pre-MP 2 >25/≤ 25 1.0 (0.6–1.7) 0.9 (0.5–1.5)
  Post-MP 2 >25/≤ 25 1.6 (1.0–2.7) 0.9 (0.4–1.7)
[12] Young 2 >24.3/≤ 24.3 1.21 (0.94–1.57) 1.03 (0.75–1.41)
[13] All women 3 ≥28/<24 1.43 (1.06–1.92) 1.19 (0.78–1.81)
  Pre-MP 3 ≥28/<24 1.08 (0.73–1.60) 1.00 (0.60–1.65)
  Post-MP 3 ≥28/<24 1.64 (1.28–2.10) 1.30 (0.89–1.89)
[14] Young 2 ≥25/<25 1.7 (1.1–2.5) 0.9 (0.6–1.4)
[7] All women 4 ≥30/<20 1.22 (0.97–1.54) 0.91 (0.68–1.22)
[8] Young 4 ≥32/<22 1.23 (0.72–2.10) 0.56 (0.30–1.07)
Summary RRs for population-based case-control studies 1.31 (1.07–1.60) 0.94 (0.76–1.15)
Hospital-based case-control studies
[15] All women Per 5 years↑ 5 years' increase 1.19 (0.93–1.51) 1.19 (0.91–1.55)
[16] All women 2 ≥30/<30 0.5 (0.2–1.2) 1.0 (0.5–1.9)
Summary RRs for hospital-based case-control studies 1.10 (0.78–1.55) 1.17 (0.83–1.65)
Summary RRs by MP status Pre-MP/Young    1.24 (0.96–1.62) 0.92 (0.71–1.20)
  Post-MP    1.65 (1.15–2.38) 1.28 (0.89–1.84)
Summary RRs for all studies 1.27 (1.07–1.50) 1.01 (0.85–1.20)
P for homogeneity between ER+PR+ and ER-PR- cancer p = 0.010
  1. Test for homogeneity across all studies: P ER+PR+ = 0.80 and P ER-PR- = 0.70. Egger's test for publication bias for all studies: P ER+PR+ = 0.83 and P ER-PR- = 0.67. CI, confidence interval; ER+, estrogen receptor-positive; ER-, estrogen receptor-negative; ER/PR, estrogen and progesterone receptor; MP, menopausal or menopause; Per 5 years↑, Per 5 years' increase in age at first birth; PR+, progesterone receptor-positive; PR-, progesterone receptor-negative; RR, relative risk.