Table 3. Relative risks of contralateral breast cancer associated with selected factors (all subjects).

Variable	Univariate RR (95% CI) P-value	Multivariatea RR (95% CI) P-value	Multivariateb RR (95% CI) P-value
Mutation
BRCA1	1.0	1.0	1.0
BRCA2	0.86 (0.62–1.20) 0.38	0.88 (0.60–1.29) 0.51	0.86 (0.61–1.22) 0.41
Age at diagnosis (years)
<40	1.0	1.0	1.0
40–49	0.78 (0.56–1.08) 0.14	0.92 (0.65–1.29) 0.61	0.91 (0.64–1.28) 0.58
⩾50	0.44 (0.26–0.73) 0.001	0.47 (0.27–0.82) 0.008	0.48 (0.28–0.82) 0.007
Oophorectomy c
No	1.0	1.0	1.0
Yes	0.49 (0.32–0.77) 0.002	0.48 (0.27–0.82) 0.002	0.53 (0.34–0.84) 0.007
Chemotherapy
No	1.0	1.0
Yes	0.87 (0.63–1.19) 0.37	0.99 (0.67–1.45) 0.94
Radiation therapy
No	1.0	1.0
Yes	1.03 (0.75–1.42) 0.84	1.11 (0.79–1.55) 0.56
Tamoxifen
No	1.0	1.0	1.0
Yes	0.64 (0.44–0.93) 0.02	0.72 (0.47–1.12) 0.14	0.74 (0.49–1.11) 0.14
ER status
Negative	1.0	1.0
Positive	0.80 (0.54–1.19) 0.26	1.02 (0.64–1.62) 0.95
Grade
I/II	1.0	1.0
III	1.00 (0.62–1.61) 0.99	0.84 (0.50–1.41) 0.51
Nodal status
Negative	1.0	1.0
Positive	0.74 (0.52–1.03) 0.08	0.76 (0.51–1.12) 0.16
First-degree relative with breast cancer ⩽50
0	1.0	1.0	1.0
1	1.27 (0.89–1.81) 0.20	1.15 (0.80–1.67) 0.45	1.19 (0.83–1.71) 0.36
2+	1.70 (1.13–2.54) 0.01	1.86 (9.22–2.83) 0.004	1.79 (1.18–2.71) 0.006
Trend	1.30 (1.06–1.59) 0.01	1.34 (1.08–1.66) 0.008	1.33 (1.08–1.64) 0.008

^aMultivariate estimates are adjusted by all variables.

^bMultivariate estimates are adjusted by four variables

^cTime dependent variable in the regression of Cox's proportional hazards model.