Reproductive factors and the risk of triple-negative breast cancer in white women and African-American women: a pooled analysis

Table 5 Multivariable adjusted odds ratio (OR) and 95% confidence interval (CI) for ER/PR/HER2-defined subtypes of breast cancer associated with duration of breastfeeding among parous women by race and age

	White women					African-American women
	Controls	Triple-negative		Luminal A-like		Controls	Triple-negative		Luminal A-like
	N	N	OR (95% CI)	N	OR (95% CI)	N	N	OR (95% CI)	N	OR (95% CI)
Younger (20–44 years)^a
Duration of breastfeeding, months
Never	85	27	1.00	57	1.00	119	37	1.00	43	1.00
Ever	383	105	0.85 (0.49–1.49)	218	0.71 (0.46–1.11)	148	37	0.43 (0.22–0.83)	48	0.58 (0.32–1.06)
<6	136	43	0.94 (0.52–1.72)	72	0.70 (0.43–1.14)	73	26	0.67 (0.33–1.36)	25	0.64 (0.32–1.26)
≥6	247	62	0.76 (0.41–1.41)	146	0.73 (0.45–1.18)	75	11	0.18 (0.07–0.46)	23	0.50 (0.24–1.06)
Trend P value			0.34		0.28			0.0004		0.07
P value for homogeneity of trends				0.93					0.09
Older (45–64 years)^b
Duration of breastfeeding, months
Never	283	39	1.00	171	1.00	261	63	1.00	96	1.00
Ever	462	74	1.06 (0.65–1.72)	374	0.83 (0.63–1.10)	249	48	0.74 (0.47–1.17)	92	0.90 (0.62–1.30)
< 6	207	41	1.30 (0.78–2.19)	158	0.91 (0.67–1.25)	125	24	0.69 (0.39–1.21)	48	0.94 (0.60–1.46)
≥ 6	255	33	0.75 (0.41–1.38)	216	0.73 (0.53–1.02)	124	24	0.81 (0.46–1.43)	44	0.85 (0.54–1.35)
Trend P value			0.41		0.07			0.35		0.49
P value for homogeneity of trends				0.85					0.72

Triple negative = estrogen receptor (ER)–/progesterone receptor (PR)–/human epidermal growth factor receptor-2 (HER2)–, Luminal A-like = ER+ and/or PR+ plus HER2. Models in multivariate analysis included sub-study (the Women’s CARE Study or Women’s BCIS Study, Women’s LIFE Study), study site (Los Angeles, Detroit), reference age (in 5-year age categories), education (< high school, technical school or some college, college graduate), first-degree breast cancer family history (no, yes), body mass index (<25, 25–29, ≥30 kg/m²), lifetime recreational physical activity (inactive, ≤2.2, 2.3–6.6, 6.7–15.1, ≥15.2 annual metabolic energy equivalents, hour/week), alcohol intake (never, former, current), cigarette smoking status (never, former, current), age at menarche (≤12,13, ≥14 years), number of completed pregnancies (1, 2, ≥3), oral contraceptive use (never, <1, 1–4, 5–9, ≥10 years) and age at first completed pregnancy (≤20, 21–24, 25–29, ≥30 years). ^aAdditionally three white younger case participants who had missing information on breastfeeding were excluded. ^bAdditionally adjusted for a variable combining menopausal status and hormone therapy use (premenopausal; postmenopausal: never used hormone therapy, ever used hormone therapy; unknown menopausal status)