Table 5.

Association of breastfeeding with breast cancer recurrence and death, stratified by median expression level of proliferation*

	<Median proliferation expression			≥Median proliferation expression
Recurrence†	No. events‡	HR	(95% CI)	No. events‡	HR	(95% CI)
Breastfeeding
Never	93	Ref.		97	Ref.
Ever	87	0.58	(0.37 to 0.93)	106	0.75	(0.46 to 1.24)
P interaction = .47
Lifetime breastfeeding
Never	93	Ref.		97	Ref.
<6 mo	38	0.71	(0.41 to 1.23)	39	0.81	(0.43 to 1.53)
≥6 mo	49	0.50	(0.29 to 0.86)	67	0.72	(0.40 to 1.27)
P trend			.03			.22
P interaction = .70
Breast cancer mortality†
Breastfeeding
Never	63	Ref.		81	Ref.
Ever	65	0.65	(0.39 to 1.09)	81	0.71	(0.40 to 1.25)
P interaction = .82
Lifetime breastfeeding
Never	63	Ref.		81	Ref.
<6 mo	32	0.85	(0.45 to 1.59)	30	0.81	(0.40 to 1.63)
≥6 mo	33	0.52	(0.29 to 0.95)	51	0.66	(0.35 to 1.26)
P trend			.08			.20
P interaction = .80

* n = 29 women had missing data on breastfeeding, parity, surgery, chemotherapy, and/or radiotherapy and were thus excluded from all models. CI = confidence interval; HR = hazard ratio.

† Adjusted for age at diagnosis, race/ethnicity, stage, chemotherapy, radiotherapy, hormonal therapy, surgery type, and parity.

‡ Not population based given case-cohort study design.