Association between air pollution and mammographic breast density in the Breast Cancer Surveilance Consortium

Breast Cancer Research

Table 2 Associations of PM_2.5 and O₃ with breast density

Exposure	BI-RADS I OR (95% CI)	BI-RADS III OR (95% CI)	BI-RADS IV OR (95% CI)
PM_2.5 quartile (median, ug/m³)^a
1^st (7.18)	Referent	Referent	Referent
2^nd (8.44)	0.95 (0.92–0.98)	1.08 (1.05–1.11)	0.90 (0.86–0.94)
3^rd (9.27)	0.85 (0.81–0.88)	1.19 (1.16–1.22)	1.00 (0.95–1.05)
4^th (10.68)	0.88 (0.85–0.92)	1.19 (1.16–1.23)	0.97 (0.92–1.02)
P for trend	<0.0001	<0.0001	<0.0001
Continuous PM_2.5	0.98 (0.97–0.99)	1.04 (1.03–1.04)	1.00 (0.99–1.01)
O₃ quartile (median, ppb)^a
1^st (28.48)	Referent	Referent	Referent
2^nd (32.94)	0.86 (0.81–0.90)	1.13 (1.10–1.16)	1.08 (1.03–1.14)
3^rd (37.03)	0.85 (0.79–0.91)	1.11 (1.07–1.16)	0.99 (0.92–1.07)
4^th (39.05)	1.12 (1.04–1.20)	0.98 (0.94–1.03)	0.80 (0.73–0.87)
P for trend	<0.0001	<0.0001	<0.0001
Continuous O₃	1.02 (1.01–1.03)	1.00 (1.00–1.01)	0.97 (0.96–0.98)

For breast density, American College of Radiology’s Breast Imaging-Reporting and Data System (BI-RADS) II (scattered fibroglandular densities) is the reference category; risk estimates are adjusted for age at mammogram, body mass index at mammogram, race, study site, age at menarche, parity and age at first birth, menopausal status/hormone use, family history of breast cancer, history of breast biopsy, and median household income for the zip code. ^aQuartiles defined as <7.91, 7.91 to <8.81, 8.81 to <9.86, and ≥9.86 ug/m³ for particulate matter <2.5 μm in diameter (PM_2.5) and <29.73, 29.73 to <36.05, 36.05 to <37.92 and ≥37.92 ppb for ozone (O₃)
CI confidence interval, HRT hormone replacement therapy, OR odds ratio. Note: BI-RADS II is the reference group

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