Table 3 Standardised incidence ratios (SIRs) of breast cancer by the number of relatives diagnosed with breast cancer at any age

From: Breast cancer risks in women with a family history of breast or ovarian cancer who have tested negative for a BRCA1 or BRCA2 mutation

Number of relatives diagnosed with breast cancer

Mean age at baseline (range)

Observed (rate per 105)

Expected (rate per 105)

SIRs

95% CI

P -value

1 or 2 (n=182)

45.9 (17–85)

9 (790.9)

1.88 (165.2)

4.79

2.52–9.10

0.001

3 (N=479)

49.6 (18–92)

23 (779.1)

5.57 (188.7)

4.13

2.75–6.20

<0.0001

4 or more (N=830)

47.9 (18–99)

32 (638.3)

9.02 (179.9)

3.55

2.51–5.01

<0.0001

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