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. 2008 Dec 16;100(2):421–425. doi: 10.1038/sj.bjc.6604830

Table 4. Standardised incidence ratios (SIRs) of breast cancer by the number of first-degree relatives diagnosed with breast cancer of ⩽50 years.

  Observed (rate per 105) Expected (rate per 105) SIRs 95% CI P-value
No first-degree relative with breast cancer of ⩽50 years (N=607) 25 (678.2) 7.11 (192.9) 3.52 2.38–5.19 <0.0001
One first-degree relative with breast cancer of ⩽50 years (N=677) 27 (646.9) 6.29 (150.7) 4.29 2.95–6.25 <0.0001
Two or more first-degree relatives with breast cancer of ⩽50 years (N=207) 12 (965.4) 3.08 (247.8) 3.90 2.23–6.81 0.0006