Fine particulate matter exposure and cancer risk: a systematic review and meta-analysis of prospective cohort studies

Studies examining the relationship between fine particulate matter (PM_2.5) exposure and cancer risk is inconclusive, with an evident scarcity of comprehensive data on the overall cancer risk. Given the emergence of new evidence, updated meta-analyses is essential. A search was performed on multiple databases including PubMed, Embase, Scopus, Web of Science, and the Cochrane Library up to Jan 2025. Hazard ratios (HRs), relative risks (RRs), or incidence rate ratios (IRRs) with their 95 % confidence intervals (CIs) were extracted and pooled. Moreover, a comprehensive and detailed quality assessment of the included studies was conducted to validate the plausibility of the findings. Overall, 57 original studies were included, covering 36 cancer categories and including overall cancer and malignancies specific to particular anatomical sites. For each increase of 10 μg per cubic meter in PM_2.5 concentration, there was an observed pooled HR of 1.07 for overall cancer (95 %CI:1.02-1.13). In the case of site-specific cancers, the pooled HRs were 1.11 (95 %CI:1.07-1.15), 1.06 (95 %CI:1.02-1.11), 1.17 (95 %CI:1.07-1.28), and 1.14 (95 %CI:1.03-1.26) for lung, breast, liver and esophageal cancers, respectively. Furthermore, PM_2.5 exposure may potentially correlate with the risk of cancers at other anatomical locations including upper aerodigestive tract, oral cavity, kidney, skin, as well as digestive organs. In light of available evidence, it is inferred that PM_2.5 exposure could potentially raise overall cancer risk with moderate certainty. As for site-specific malignancies, there is very low certainty evidence for lung cancer, low certainty evidence for breast cancer, and moderate certainty evidence for both liver and esophageal cancers.