Air pollution with NO, PM, and elemental carbon in relation to risk of breast cancer- a nationwide case-control study from Denmark.

UNLABELLED

Air pollution with particulate matter is an established lung carcinogen. Studies have suggested an association with breast cancer, but the evidence is inconsistent.

METHODS

From nationwide registers, we identified all breast cancer cases (n = 55 745) in Denmark between 2000 and 2014. We matched one control for each case on age and year of birth. We used a multi-scale dispersion model to estimate outdoor concentrations of particulate matter <2.5 μm (PM), elemental carbon (EC) and nitrogen dioxide (NO) as time-weighted average over all addresses up to 20 years prior to diagnosis. We calculated odds ratios (OR) and 95% confidence intervals (CI) by conditional logistic regression with adjustment for marital status, educational level, occupational status, personal income, region of origin, medication and area-level socio-economic indicators.

RESULTS

A 10 μg/m higher PM was associated with an OR for breast cancer of 1.21 (95% CI: 1.11-1.33). The corresponding ORs for EC (per 1 μg/m) and NO (per 10 μg/m) were 1.03 (95% CI: 1.00-1.07) and 1.03 (95% CI: 1.01-1.06), respectively. In multi-pollutant models, the OR for PM changed only little, whereas ORs for EC or NO approached the null. In an analysis of persons below 55 years, PM was associated with an OR of 1.32 (95% CI: 1.09-1.60) per 10 μg/m increase.

CONCLUSION

We found evidence of an association between the investigated air pollutants and breast cancer, especially PM. There were indications that the association differed by age at diagnosis. We were not able to include all potential confounders and thus, results should be interpreted with caution.