Table 3.

Reproductive factors in relation to ER+/PR+ and ER−/PR− breast cancer by age

	ER + / PR +				ER − / PR −
	Age < 45		Age ≥ 45		Age < 45		Age ≥ 45
	Cases	HR (95% CI)	Cases	HR (95% CI)	Cases	HR (95% CI)	Cases	HR (95% CI)
Number of births
0	31	1.00 (Reference)	79	1.00 (Reference)	29	1.00 (Reference)	27	1.00 (Reference)
1	36	0.90 (0.47–1.71)	76	0.68 (0.48–0.98)	22	0.81 (0.41–1.59)	42	1.17 (0.69–1.96)
2	25	0.71 (0.37–1.39)	111	0.73 (0.53–1.01)	31	1.37 (0.74–2.56)	76	1.61 (1.01–2.57)
≥ 3	14	0.76 (0.36–1.59)	85	0.47 (0.33–0.66)	23	1.89 (1.00–3.59)	66	1.39 (0.86–2.25)
	P trend = 0.32		P trend < 0.0001		P trend = 0.02		P trend = 0.11
Age at 1st birth
< 20	16	1.00 (Reference)	87	1.00 (Reference)	17	1.00 (Reference)	65	1.00 (Reference)
20–24	13	0.69(0.33–1.46)	93	0.93 (0.69–1.26)	19	1.13 (0.52–1.99)	63	0.93 (0.65–1.33)
25–29	20	1.23 (0.61–2.49)	60	1.22 (0.86–1.73)	21	1.66 (0.61–2.59)	38	1.21 (0.79–1.86)
≥ 30	26	1.75 (0.85–3.61)	32	1.14 (0.73–1.79)	19	2.24 (0.76–3.86)	18	1.16 (0.65–2.07)
	P trend = 0.04		P trend = 0.31		P trend = 0.03		P trend = 0.42
Years since last birth
≥ 15	20	1.00 (Reference)	244	1.00 (Reference)	14	1.00 (Reference)	170	1.00 (Reference)
10–14	11	0.71 (0.33–1.51)	15	1.15 (0.65–2.03)	20	1.84 (0.90–3.74)	9	1.01 (0.49–2.05)
< 10	43	1.61 (0.88–2.95)	8	1.51 (0.71–3.23)	42	2.18 (1.08–4.41)	2	0.66 (0.16–2.79)
	P trend = 0.08		P trend = 0.23		P trend = 0.03		P trend = 0.66
Ever breastfed
No	32	1.00 (Reference)	160	1.00 (Reference)	40	1.00 (Reference)	122	1.00 (Reference)
Yes	43	1.30 (0.80–2.12)	108	1.10 (0.85–1.42)	36	0.78 (0.48–1.26)	59	0.79 (0.57–1.09)

HRs were derived from models that adjusted for age, time, geographic region, age at menarche, age at menopause, use of menopausal hormone supplements, use of oral contraceptives, body mass index, physical activity, alcohol intake, cigarette smoking, family history of breast cancer, and each of the other reproductive factors.