Table 4.

Association of breastfeeding with breast cancer recurrence and death, stratified by PAM50 intrinsic subtype*

	Luminal A			Luminal B			Basal-like			HER2-E
Recurrence†	No. events‡	HR	(95% CI)	No. events‡	HR	(95% CI)	No. events‡	HR	(95% CI)	No. events‡	HR	(95% CI)
Breastfeeding
Never	67	Ref.		61	Ref.		33	Ref.		29	Ref.
Ever	65	0.52	(0.31 to 0.89)	62	0.60	(0.26 to 1.41)	24	0.64	(0.24 to 1.72)	42	1.29	(0.44 to 3.82)
P interaction = .19
Lifetime breastfeeding
Never	67	Ref.		61	Ref.		35	Ref.		29	Ref.
<6 mo	29	0.67	(0.34 to 1.30)	21	0.70	(0.24 to 2.00)	12	1.34	(0.41 to 4.37)	15	1.01	(0.26 to 3.91)
≥6 mo	36	0.43	(0.23 to 0.79)	41	0.55	(0.21 to 1.44)	12	0.39	(0.14 to 1.07)	27	1.58	(0.51 to 4.92)
P trend			.03			.15			.04			.54
P interaction = .11
Breast cancer mortality†
Breastfeeding
Never	53	Ref.		42	Ref.		28	Ref.		21	Ref.
Ever	47	0.52	(0.29 to 0.93)	49	0.61	(0.24 to 1.56)	20	0.70	(0.18 to 2.79)	30	1.29	(0.35 to 4.77)
P interaction = .21
Lifetime breastfeeding
Never	53	Ref.		42	Ref.		28	Ref.		21	Ref.
<6 mo	22	0.68	(0.33 to 1.43)	18	0.78	(0.25 to 2.37)	9	1.22	(0.26 to 5.72)	13	1.23	(0.28 to 5.39)
≥6 mo	25	0.42	(0.22 to 0.83)	31	0.53	(0.18 to 1.54)	11	0.49	(0.13 to 1.90)	17	1.35	(0.29 to 6.40)
P trend			.08			.12			.17			.92
P interaction = .39

* n = 27 women had missing data on parity, surgery, chemotherapy, and/or radiotherapy and were thus excluded from all models.

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

‡ Not population based given case-cohort study design.