Table 1. Childhood cancer risks in relation to breastfeeding in infancy, OSCC data, 1972–1981 deaths.

Breastfeeding history	Cases	Controls	ORa	(95% CI)	ORb	(95% CI)	ORc	(95% CI)
Acute lymphocytic leukaemia (ALL) (n=948)
Never	480	490	1.0				1.0
Ever breastfed	461	452	1.04	(0.86–1.26)	0.99	(0.82–1.20)	1.05	(0.90–1.21)
Breastfed
<1 month	151	137	1.15	(0.87–1.51)	1.10	(0.83–1.46)	1.16	(0.93–1.43)
1–6 months	241	246	1.01	(0.81–1.26)	0.96	(0.77–1.20)	0.96	(0.80–1.15)
⩾7 months	62	66	0.97	(0.66–1.43)	0.90	(0.60–1.34)	1.09	(0.80–1.48)
Unknown duration	7	3	—
Not known	7	6	—
P-value for trendd			P=1.00	P=0.55	P=0.99
Other leukaemia (n=394)
Never	205	208	1.0				1.0
Ever breastfed	187	181	1.06	(0.78–1.45)	1.03	(0.74–1.43)	0.99	(0.80–1.23)
Breastfed
<1 month	51	40	1.29	(0.82–2.04)	1.24	(0.77–1.98)	0.95	(0.68–1.32)
1–6 months	105	114	0.94	(0.66–1.35)	0.90	(0.62–1.31)	0.97	(0.76–1.25)
⩾7 months	30	26	1.16	(0.65–2.07)	1.16	(0.64–2.11)	1.17	(0.77–1.77)
Unknown duration	1	1	—
Not known	2	5	—
P-value for trendd			P=0.81	P=0.92	P=0.71
Leukaemia (n=1342)
Never	685	698	1.0				1.0
Ever breastfed	648	633	1.05	(0.89–1.23)	1.00	(0.85–1.18)	1.03	(0.91–1.18)
Breastfed
<1 month	202	177	1.18	(0.93–1.50)	1.14	(0.89–1.45)	1.10	(0.91–1.33)
1–6 months	346	360	0.99	(0.82–1.19)	0.95	(0.79–1.15)	0.97	(0.83–1.13)
⩾7 months	92	92	1.03	(0.75–1.43)	0.98	(0.71–1.37)	1.11	(0.85–1.44)
Unknown duration	8	4	—
Not known	9	11	—
P-value for trendd			P=0.90	P=0.70	P=0.84
Other reticuloendothelial cancers (n=326)e
Never	160	182	1.0				1.0
Ever breastfed	163	142	1.34	(0.97–1.87)	1.32	(0.93–1.89)	1.10	(0.87–1.39)
Breastfed
<1 month	56	49	1.35	(0.85–2.13)	1.38	(0.86–2.25)	1.28	(0.92–1.77)
1–6 months	84	74	1.37	(0.92–2.06)	1.33	(0.86–2.06)	0.99	(0.75–1.31)
⩾7 months	23	18	1.53	(0.78–3.00)	1.56	(0.75–3.21)	1.23	(0.77–1.97)
Unknown duration	0	1	—
Not known	3	2	—
P-value for trendd			P=0.07	P=0.11	P=0.62
All other cancers (n=1708)
Never	901	901	1.0		1.0		1.0
Ever breastfed	777	797	0.98	(0.84–1.13)	0.95	(0.82–1.11)	0.97	(0.86–1.10)
Breastfed
<1 month	228	236	0.97	(0.79–1.20)	0.94	(0.76–1.17)	0.98	(0.82–1.17)
1–6 months	441	457	0.97	(0.81–1.15)	0.94	(0.79–1.12)	0.97	(0.84–1.12)
⩾7 months	105	101	1.04	(0.77–1.41)	1.06	(0.78–1.45)	0.96	(0.74–1.23)
Unknown duration	3	3	—
Not known	30	10	—
P-value for trendd			P=0.96	P=0.85	P=0.57
All childhood cancers (n=3376)
Never	1746	1781	1.0		1.0		1.0
Ever breastfed	1588	1572	1.04	(0.93–1.15)	1.01	(0.91–1.12)	1.01	(0.91–1.11)
Breastfed
<1 month	486	462	1.08	(0.93–1.25)	1.05	(0.90–1.22)	1.05	(0.91–1.22)
1–6 months	871	891	1.00	(0.89–1.13)	0.98	(0.87–1.11)	0.97	(0.87–1.09)
⩾7 months	220	211	1.07	(0.87–1.32)	1.06	(0.85–1.31)	1.04	(0.85–1.27)
Unknown duration	11	8	—
Not known	42	23	—
P-value for trendd			P=0.55	P=0.77	P=0.94

^aObtained from conditional logistic regression applied to matched pairs.

^bObtained from conditional logistic regression applied to matched pairs with additional adjustment for social class based on paternal occupation (five levels: I, II, III, IV, V), age of mother at birth of survey child (six levels: <20, 20–24, 25–29, 30–34, 35–39, ⩾40 years), and sibship position (five levels: 1, 2, 3, 4, ⩾5).

^cObtained from unconditional logistic regression using all controls for comparison group, adjusted for sex of child, age at death (or corresponding age for controls) (1–4, 5–9, 10–14 years), social class, maternal age at birth of child and sibship position.

^dP-value for trend across four levels of breastfeeding history variable (never, <1, 1–6, ⩾7 months) levels scored 1–4.

^eComprising lymphosarcoma, Hodgkin's disease, reticulosarcoma, giant follicular lymphoma, storage reticulosis, histiocytic reticulosis, chloroma and Burkitt's lymphoma.