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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.