The association between ambient air pollution exposure and
lung cancer risk has been investigated in prospective studies and the results are generally consistent, indicating that long-term exposure to air pollution may cause
lung cancer. Despite the prospective nature and consistent findings of these studies, causality assessment can benefit from
biomarker research. In the present systematic review, we assess the contribution of intermediate
biomarkers in epidemiological studies, to ascertain whether their measurement reinforces causal reasoning. We have reviewed 524 papers which described the relationships between ambient air pollution and
biological markers of dose and early response. The evidence for each marker was evaluated using assessment criteria which rate a group of studies from A (strong) to C (weak) on amount of evidence, replication of findings, and protection from bias.
Biomarkers that scored A or B for all three criteria are included here. The markers that fulfilled the inclusion criteria are:
1-hydroxypyrene,
DNA adducts,
chromosomal aberrations, micronuclei, oxidative damage to nucleobases, and methylation changes. These
biomarkers cover the whole spectrum of disease onset and progression from external exposure to tumour formation and some have also been suggested as risk predictors of future
cancer, reinforcing causal reasoning. However, methodological issues such as confounding, publication bias and use of surrogate tissues instead of target tissues in studies on these markers are of concern. The identified
biological markers have potential to shed light on the pathways of
carcinogenesis, thus defining the association more clearly for public health interventions.