Table 6.

Random-effects meta-analysis for the association between a $10\text{-}{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ increase in exposure to nitrogen dioxide (${\mathrm{NO}}_2$) and breast cancer onset: main analyses, sensitivity analyses (SA, based on the main analysis not corrected for publication bias), and supplementary analyses according to the menopausal status or the hormonal receptor subtype.

Meta-analysis	$n$ effect estimates	$n$ cases	$n$ participants	RR (95% CI)	$I^2$ (%)	Heterogeneity $p$-valuea
Main analysis (not corrected for publication bias)b,c	22	121,189	3,922,395	1.027 (1.009, 1.047)	24.0	0.15
Main analysis (corrected for publication bias)b,c	28	123,263d	3,939,096d	1.023 (1.005, 1.041)	23.0	0.14
SA1. Leave-one-out meta-analysise,c	21	111,612	2,901,363	1.019 (1.003, 1.036)	12.1	0.41
SA2. Restricted to prospective cohort studiese	16	16,668	329,318	1.020 (1.000, 1.041)	4.9	0.56
SA3. Restricted to European populations	14	15,500	1,121,165	1.042 (1.009, 1.075)	5.1	0.62
SA4. Restricted to North American populationse	8	105,689	2,801,230	1.024 (0.999, 1.049)	46.3	0.11
SA5. Restricted to studies with adjustment for main reproductive factorsf	5	7,150	87,372	1.020 (0.986, 1.055)	3.1	0.67
SA6. Restricted to studies with adjustment for socioeconomic contextg,c	18	109,035	2,870,731	1.019 (1.003, 1.036)	10.5	0.47
SA7. Restricted to effect estimates reported in “all women” onlyh	7	110,009	3,718,900	1.032 (1.005, 1.061)	54.9	0.035
SA8. Excluding the effect estimate reported in premenopausal women from CNBSS	21	120,537	3,884,185	1.025 (1.006, 1.043)	21.6	0.20
SA9. Excluding CECILE case–control study (not published yet)e	21	120,024	3,919,959	1.026 (1.007, 1.044)	23.0	0.17
SA10. Restricted to studies with exposure assessment based on precise home addressesi,c	20	20,466	337,023	1.026 (1.005, 1.047)	7.6	0.47
SA11. Restricted to studies with exposure assessment based on residential historyj	5	97,615	2,650,435	1.012 (0.991, 1.033)	14.1	0.62
SA12. Restricted to studies which started since 2000k	6	105,454	3,638,449	1.055 (1.002, 1.112)	62.4	0.008
In premenopausal women	4	2,065	NAl	1.059 (0.985, 1.138)	15.4	0.38
In postmenopausal women	17	14,050	NAl	1.019 (0.993, 1.046)	5.0	0.63
Hormone responsive positive ($\text{ER}+/\text{PR}+$)	4	4,460	NAl	1.045 (0.980, 1.114)	15.9	0.40
Hormone responsive negative ($\text{ER}–/\text{PR}–$)	4	NAl	NAl	0.987 (0.885, 1.101)	19.6	0.28

Note: Studies included in sensitivity analyses (SA): SA1: All but AOK PLUS; SA2: CEANS, CNBSS, DCH, DNC, EPIC-E3N, EPIC-NL, EPIC-Oxford, EPIC-San Sebastian, EPIC-Turin, EPIC-Umeå, EPIC-Varese, HUBRO, MEC, Sister Study, VHM&PP; SA3: AOK PLUS, CEANS, CECILE, DCH, DNC, EPIC-E3N, EPIC-NL, EPIC-Oxford, EPIC-San Sebastian, EPIC-Turin, EPIC-Umeå, EPIC-Varese, HUBRO, VHM&PP; SA4: CCSPBCM1, CCSPBCM2, CNBSS, MEC, NECSS, ONPHEC, Sister Study; SA5: CCSPBCM2, CECILE, DNC, MEC, NECSS; SA6: CCSPBCM1, CCSPBCM2, CEANS, CNBSS, DCH, EPIC-NL, EPIC-Oxford, EPIC-San Sebastian, EPIC-Turin, EPIC-Umeå, EPIC-Varese, HUBRO, MEC, NECSS, ONPHEC, Sister Study, VHM&PP; SA7: AOK PLUS, CECILE, DNC, MEC, NECSS, ONPHEC, Sister Study; SA8: All studies without the effect estimate reported in premenopausal women from CNBSS; SA9: All but CECILE; SA10: CCSPBCM1, CCSPBCM2, CEANS, CECILE, CNBSS, DCH, DNC, EPIC-E3N, EPIC-NL, EPIC-Oxford, EPIC-San Sebastian, EPIC-Turin, EPIC-Umeå, EPIC-Varese, HUBRO, MEC, NECSS, Sister Study, VHM&PP; SA11: CECILE, DNC, MEC, NECSS, ONPHEC; SA12: AOK PLUS, CCSPBCM2, CECILE, HUBRO, ONPHEC, Sister Study; In premenopausal women: CECILE, CNBSS, NECSS, Sister Study; In postmenopausal women: CCSPBCM1, CCSPBCM2, CEANS, CECILE, CNBSS, DCH, EPIC-E3N, EPIC-NL, EPIC-Oxford, EPIC-San Sebastian, EPIC-Turin, EPIC-Umeå, EPIC-Varese, HUBRO, NECSS, Sister Study, VHM&PP; On hormonal receptor subtypes: CCSPBCM2, CECILE, MEC, Sister Study: .

^aCochrane’s heterogeneity Q test.

^bEffect estimates reported in studies led in postmenopausal women only were included in the main meta-analysis in addition to the effect estimates reported in “all women” (i.e., irrespective of menopausal status).

^cBecause no global effect estimate was available in “all women” from CNBSS, both effect estimates reported separately in postmenopausal and premenopausal CNBSS women were included.

^dEffectives simulated by trim-and-fill analysis.

^eIt means, excluding the study contributing the most to the between-study heterogeneity (Figure S3).

^fAge at menarche, age at the first full-term pregnancy, and parity.

^gAt the area level.

^hI.e., irrespective of menopausal status.

ⁱI.e., excluding studies in which air pollutant levels were assessed at the postal code scale.

^jI.e., excluding studies in which air pollutant levels were assessed for a single home address.

^kBecause of stronger potential for exposure misclassification in studies recruiting subjects before 2000.

^lSample size could not be calculated due to missing information in source studies.