Table 3.

Case-only odds ratios and 95% confidence intervals from logistic regression models^a of associations between breast cancer tumor subtypes and demographic, reproductive, and lifestyle risk factors, combined LACE and Pathways Studies (n = 2544)

	Luminal A (comparison)	Luminal Ba
	n	N	OR	95% CI
Age at diagnosis (years)
≥ 65 (Ref)	637	82	Ref	---
50 to 64	871	124	1.09	0.81, 1.47
< 50	355	88	1.83	1.32, 2.55
Test for trend				P = 0.0001
Race/ethnicity
White (Ref)	1464	215	Ref	---
African American	92	14	0.97	0.54, 1.74
Hispanic	135	28	1.32	0.85, 2.04
Asian	135	30	1.38	0.90, 2.12
Other	37	7	1.29	0.56, 2.94
Menopausal status				---
Postmenopausal (Ref)	1283	173	Ref
Premenopausal	406	95	1.32	0.87, 2.00
Family history
No (Ref)	1453	245	Ref	---
Yes	410	49	0.74	0.53, 1.02
Age at first full-term pregnancy (years)
Nulliparous (Ref)	335	51	Ref	---
< 26	959	158	1.25	0.88, 1.78
≥ 26	567	85	1.04	0.72, 1.52
Parity
Nulliparous (Ref)	335	51	Ref	---
1 to 2 children	837	150	1.24	0.88, 1.76
≥ 3 children	691	93	1.03	0.70, 1.50
Lifetime duration of breastfeeding
Never (Ref)	871	135	Ref	---
0 to 3 months	255	50	1.31	0.92, 1.88
≥ 4 months	711	100	0.86	0.65, 1.14
Parity among never breastfedb
Nulliparous (Ref)	321	50	Ref	---
1 to 2 children	326	59	1.38	(0.89, 2.13)
≥ 3 children	224	26	1.01	(0.58, 1.76)
Parity among 0 to 3 months breastfedb
1 to 2 children (Ref)	144	33	Ref	---
≥ 3 children	108	17	0.90	(0.45, 1.77)
Parity among ≥ 4 months breastfedb
1 to 2 children (Ref)	358	56	Ref	---
≥ 3 children	352	44	0.84	(0.54, 1.32)
Alcohol use
Never (Ref)	709	131	Ref	---
Ever	880	119	0.74	0.56, 0.98
Smoking history
Never (Ref)	921	163	Ref	---
≤ 10	251	39	0.86	0.59, 1.27
11 to 19	147	22	0.93	0.57, 1.51
≥ 20	531	68	0.80	0.59, 1.09
Hormone replacement therapy (postmenopausal only)
Never (Ref)	314	55	Ref	---
Ever	943	114	0.66	0.46, 0.94
Oral contraceptive use
Never (Ref)	647	110	Ref	---
Ever	1160	172	0.73	0.55, 0.96
BMI (kg/m2)c
< 25 (Ref)	785	134	Ref	---
25 to 29	563	79	0.92	0.67, 1.24
≥ 30	500	77	1.03	0.75, 1.41
BMI (kg/m2) among premenopausalb
< 25 (Ref)	223	50	Ref	---
25 to 29	99	21	1.11	0.62, 2.00
≥ 30	81	24	1.68	0.92, 3.07
BMI (kg/m2) among postmenopausalb
< 25 (Ref)	480	67	Ref	---
25 to 29	422	52	0.90	0.61, 1.33
≥ 30	372	50	0.99	0.66, 1.47

^a Adjusted for age at diagnosis, race/ethnicity, and Pathways/LACE study origin except in models with age at diagnosis or race/ethnicity as main predictors.

^b P for interaction not statistically significant (P > 0.05) in any tumor subtype model.

^c BMI = body mass index one year pre-diagnosis (LACE) and around diagnosis (Pathways).

CI = confidence interval; OR = odds ratio.