The roles of ambient fine particulate matter (PM2.5) in the prevention of colorectal cancer (CRC) have been scarcely highlighted as there is short of empirical evidence regarding the influences of PM2.5 on multistep carcinogenic processes of CRC. A retrospective cohort design with multistate outcomes was envisaged by linking monthly average PM2.5 concentrations at 22 city/county level with large-scale cohorts of cancer-screened population to study the influences of PM2.5 on short-term inflammatory process and multistep carcinogenic processes of CRC. Our study included a nationwide CRC screening cohort of 4,628,995 aged 50-69 years who attended first screen between 2004 and 2009 and continued periodical screens until 2016. We aimed to illustrate the carcinogenesis of PM2.5 related to CRC by applying both hierarchical logistical and multistate Markov regression models to estimate the effects of air pollution on fecal immunochemical test (FIT) positive (a proxy of inflammatory marker) and pre-clinical and clinical states of CRC in the nationwide cohort. We found a significant association of high PM2.5 exposure and FIT-positive by an increased risk of 11% [95% confidence interval (CI), 10-12]. PM2.5 enhanced the risk of being preclinical state by 14% (95% CI, 10-18) and that of subsequent progression from pre-clinical to clinical state by 21% (95% CI, 14-28). Furthermore, the elevated risks for CRC carcinogenesis were significantly higher for people living in high PM2.5 pollution areas in terms of yearly averages and the number days above 35 µg/m3 than those living in low PM2.5 pollution areas. We concluded that both short-term and long-term PM2.5 exposure were associated with multistep progression of CRC, which were useful to design precision primary and secondary prevention strategies of CRC for people who are exposed to high PM2.5 pollution.
Keywords: carcinogenesis; cohort study; colorectal cancer; fecal hemoglobin concentration; fine particulate matter.