Table 5.

Pooled odds ratios and 95% confidence intervals for breast cancer molecular subtype associated with common risk factors.

Risk factors	Nstudy	Ncontrol	Luminal			ER-PR-			PH1b	Nstudy	Ncontrol	HER2-enriched			Triple-negative			PH2c
			Ncase	ORpooled	Pha	Ncase	ORpooled	Pha				Ncase	ORpooled	Pha	Ncase	ORpooled	Pha
BMI, kg/m2
<18.5	3	415	110	1.00		35	1.00			–	–	–	–	–	–	–	–
18.5–24.9	3	4210	1432	1.20 (0.96–1.49)	0.68	553	1.43 (1.00–2.05)	0.57	0.66	–	–	–	–	–	–	–	–
≥25	3	1349	534	1.75 (1.30–2.35)	0.22	191	1.95 (1.04–3.65)	0.07	0.87	–	–	–	–	–	–	–	–
			Ptrend<0.001d			Ptrend = 0.03d
Menopausal age, years
<50	3	1261	547	1.00		260	1.00			–	–	–	–	–	–	–	–
≥50	3	1363	682	1.15 (1.00–1.32)	0.26	369	1.19 (1.00–1.43)	0.06	0.32	–	–	–	–	–	–	–	–
Age at menarche, years
>12	4	5968	2146	1.00		948	1.00			3	3773	265	1.00		505	1.00
≤12	4	1307	525	1.39 (1.23–1.57)	0.28	168	1.20 (0.91–1.58)	0.11	0.01	3	616	28	0.76 (0.50–1.16)	0.15	59	1.28 (0.94–1.73)	0.76	0.001
Parity
≥1	6	10,604	5032	1.00		2012	1.00			4	4684	364	1.00		730	1.00
0	6	771	408	1.26 (1.11–1.44)	0.14	128	1.03 (0.84–1.26)	0.28	0.04	4	406	38	1.02 (0.70–1.47)	0.19	50	1.34 (0.96–1.85)	0.66	0.10
Age at first live birth, years
<25	5	3829	1592	1.00		821	1.00			3	1628	119	1.00		306	1.00
≥25	5	6087	3093	1.14 (0.86–1.52)e	<0.001	1149	0.83 (0.62–1.10)e	<0.001	<0.001	3	2443	160	0.93 (0.56–1.56)e	<0.001	361	0.80 (0.56–1.14)e	<0.001	<0.001
Breastfeeding
Yes	5	8430	3806	1.00		1529	1.00			3	3626	222	1.00		585	1.00
No	5	1579	851	1.35 (1.05–1.74)e	<0.001	186	1.74 (1.41–2.15)	0.23	<0.001	3	484	48	1.97 (1.39–2.80)	0.23	78	1.85 (1.06–3.21)e	0.02	0.07

^aP-values (two-sided) were based on a Q-test of heterogeneity between included studies.

^bP_H1: P-value of heterogeneity of exposure-disease ORs among luminal and ER−/PR− subtypes.

^cP_H2: P-value of heterogeneity of exposure-disease ORs among luminal, HER2-enriched and triple-negative subtypes.

^dP-value for trends calculated by trend chi-square.

^eThe pooled odds ratio was calculated by a random-effects model.