Table 3.

The effect of the various patterns of breast cancer in the family on the age of onset of breast cancer in the women under study (multivariate)

Family characteristics	Relative risk at age 30 *	95% C.I. of relative risk at age 30	Change of relative risk per 10 years **	Overall Significance ***
≥ 2 cases of female breast cancer in first or second-degree relatives (yes vs. no)	3.09	1.28–7.44	0.745
≥ 2 cases of female breast cancer under age 50 (yes vs. no)	3.36	1.12–10.08	0.489
≥ 1 case of female breast cancer under age 40 (yes vs. no)	2.06	0.83–5.12	1.000
Bilateral breast cancer in affected sister (index patient) (yes vs. no)	3.47	1.33–9.05	0.834	< .001
Model score ****
0 *****	1
1	2.01	(0.89–4.55)	0.942
≥ 2	10.62	(4.22–26.72)	0.430	<.001

* Due to low prevalence, the hazard ratio can be considered as a relative risk.

** The relative risk at age 30 can be multiplied with this factor for calculating the relative risk at age 40, age 50 and so on.

*** Model significance was based on the likelihood ratio of the final model as compared to the O-model without any covariate.

**** Model score based on the family characteristics included in the multivariate model, each characteristic present yields one point.

***** Reference category.