Association of air pollution with postmenopausal breast cancer risk in UK Biobank.

Background: We investigated the association of several air pollution measures with postmenopausal breast cancer (BCa) risk.

Methods: This study included 155,235 postmenopausal women (of which 6146 with BCa) from UK Biobank. Cancer diagnoses were ascertained through the linkage to the UK National Health Service Central Registers. Annual exposure averages were available from 2005, 2006, 2007, and 2010 for NO₂, from 2007 and 2010 for PM₁₀, and from 2010 for PM_2.5, NO_X, PM_2.5-10 and PM_2.5 absorbance. Information on BCa risk factors was collected at baseline. Cox proportional hazards regression was used to evaluate the associations of year-specific and cumulative average exposures with BCa risk, overall and with 2-year exposure lag, while adjusting for BCa risk factors.

Results: PM₁₀ in 2007 and cumulative average PM₁₀ were positively associated with BCa risk (2007 PM₁₀: Hazard ratio [HR] per 10 µg/m³ = 1.18, 95% CI 1.08, 1.29; cumulative average PM₁₀: HR per 10 µg/m³ = 1.99, 95% CI 1.75, 2.27). Compared to women with low exposure, women with higher 2007 PM₁₀ and cumulative average PM₁₀ had greater BCa risk (4th vs. 1st quartile HR = 1.15, 95% CI 1.07, 1.24, p-trend = 0.001 and HR = 1.35, 95% CI 1.25, 1.44, p-trend < 0.0001, respectively). No significant associations were found for any other exposure measures. In the analysis with 2-year exposure lag, both 2007 PM 10 and cumulative average PM10 were positively associated with BCa risk (4th vs. 1st quartile HR = 1.19, 95% CI 1.10, 1.28 and HR = 1.29, 95% CI 1.19, 1.39, respectively).

Conclusion: Our findings suggest a positive association of 2007 PM₁₀ and cumulative average PM₁₀ with postmenopausal BCa risk.