Table 4.

Modeled age at breast cancer diagnosis by gene and risk factor status and p-values for gene effects (G), environmental factor effects (E) and gene by environment (GxE) interations.

Risk Factor	Categories	BRCA1+	BRCA2+	BRCA−	P-values
# of full-term pregnancies	0	38.2	41.9	41.3	G: <0.0001
	1	39.1	40.5	42.0	E: <0.0001
	2	41.8	44.5	44.3	GxE: 0.91
	≥3	42.8	44.7	46.1
Age at last pregnancy	<20 years	41.2	43.6	45.2	G: 0.0004
	20–24 years	41.7	46.6	45.5	E: 0.0087
	25–29 years	41.8	40.8	43.3	GxE: 0.37
	≥30 years	40.6	42.7	43.4
Age at menarche	<12 years	41.4	43.9	43.5	G: 0.0001
	12 to 14 years	40.2	42.3	43.2	E: 0.34
	>14 years	40.0	43.4	42.9	GxE: 0.86
Oral contraceptive duration of use	<12 months	43.8	45.2	44.8	G: <0.0001
	12–35 months	38.8	41.6	44.4	E. <0.0001
	36–59 months	38.3	44.6	43.5	GxE: 0.20
	>60 months	39.6	41.9	42.2
Breastfed	Never	42.1	45.3	46.7	G: 0.0016
	Ever	41.3	42.4	43.8	E: 0.014 GxE: 0.60
BMI kg/m2 (1 year before diagnosis)	<25	40.3	43.1	42.9	G: 0.0004
	25 – <30	41.6	42.6	43.4	E: 0.13
	≥30	41.3	45.7	45.9	GxE: 0.14
BMI kg/m2 (at age 18)	Underweight	40.9	44.2	45.5	G: 0.0048
	Normal	37.6	41.5	39.2	E: 0.0076
	Overweight	40.9	42.9	43.2	GxE: 0.65
Alcohol Use	Yes	39.8	42.6	43.1	G: 0.015
	No	42.7	44.3	42.8	E: 0.031 GxE: 0.047
Smoking status	Never	40.7	42.8	42.7	G: <0.0001
	Ever	40.3	43.2	44.0	E: 0.54 GxE: 0.34