Table 4:

Risk factor associations by ER status among women ≥50 years of age among 398 cases and 802 controls

				ER-positive N = 205				ER-negative N = 193				ER-negative/ER-positive
	Controls	ER-positive	ER-negative	OR	95% CI		p-trend	OR	95% CI		p-trend	p-het
Age at menarche (years)
<15	177	51	39	1·00				1·00
15	225	50	46	0·69	0·43	0·85		0·85	0·51	1·39		0·60
16	145	37	27	0·73	0·43	0·69		0·69	0·39	1·22		0·84
≥17	146	42	43	0·84	0·50	1·13	0·74	1·13	0·67	1·92	0·77	0·36
Parity
Nulliparous	19	12	14	1·00				1·00
1–2	127	48	36	0·82	0·31	2·16		0·34	0·13	0·88		0·13
3–4	256	72	53	0·58	0·23	1·49		0·23	0·09	0·57		0·83
≥5	406	76	91	0·49	0·19	1·26	0·24	0·28	0·11	0·70	0·004	0·33
Age at first birth (years)
<19	245	46	50	1·00				1·00
19–21	220	49	56	1·10	0·67	1·78		1·26	0·80	2·00		0·55
22–25	165	48	42	1·10	0·66	1·83		1·06	0·64	1·75		1·00
≥26	118	32	24	1·09	0·61	1·93	0·72	1·02	0·57	1·84	0·95	0·84
Median months breastfeeding per pregnancy (among parous women)
<13	163	68	42	1·00				1·00
13–18	276	54	53	0·61	0·39	0·95		0·81	0·50	1·30		0·35
≥19	313	51	66	0·54	0·34	0·85	0·01	0·89	0·56	1·42	0·82	0·07

Polytomous logistic regression models were adjusted for age, education, study site, body size, family history of breast cancer, menopausal status, age at menopause, and all reproductive factors listed above. P-values <0·05 were considered statistically significant. ER=oestrogen receptor. OR=odds ratio. CI=confidence index. P-het=p-heterogeneity test.