Exposure to Particulate Matter Air Pollution and the Incidence and Mortality of GI Cancers: A Systematic Review

PURPOSE High levels of particulate matter (PM) air pollution increase the risk of developing cardiovascular diseases, asthma, and cancer. Outdoor air pollution, especially PM, is classified as a human carcinogen on the basis of associations with lung cancer, but research investigating other cancer sites is limited. This systematic review investigates the scope and quality of existing literature on PM and the incidence and mortality of GI cancers. METHODS This review was conducted in accordance with the PRISMA protocol guidelines and submitted under PROSPERO ID: 139597. Initial searches of 5 databases yielded 2,041 articles, of which 762 duplicates were removed. Eligible studies evaluated an association between PM and at least one GI cancer. The titles and abstracts of 1,279 articles were screened independently and 102 articles were selected for additional screening. Ten studies were included in the final analysis. We evaluated the overall quality of included studies using GRADE criteria. RESULTS All articles meeting the criteria for inclusion were of cohort study design and published in 2015 or later. Methods for assessing PM exposure varied. More than one half (n = 6) of the studies investigated liver cancer. Most met the GRADE criteria for moderate certainty or greater. Six studies found a statistically significant positive association, and none found evidence of a negative association. CONCLUSION Evidence of a positive association between the incidence and mortality of GI cancers exists; however, few studies have evaluated this association. Methods of assessing exposure are highly variable. Future researchers should strive to conduct more studies in the most affected geographic areas to evaluate the impact of different PM exposure assessment approaches on observed associations, and include the evaluation of cancer subtypes and specific chemical components of PM.