O-063 Endocrine Disrupting Chemicals and Colorectal Cancer – An Analysis of Four Participating Cohorts of the Canadian Partnership for Tomorrow’s Health Study

Introduction Endocrine disrupting chemicals (EDCs) may influence cancer risk by interfering with sex hormone signaling but their role in colorectal cancer (CRC) etiology is under-explored. EDCs are ubiquitous in the general environment, but exposure levels are much higher in some workplaces. Methods Occupational EDC exposure in relation to CRC was examined in the Canadian Partnership for Tomorrow’s Health, a collaboration of six Canadian regional cohorts, including 330,000 participants aged 30-74 at baseline. Among four regional cohorts with enough cases for inclusion, a case-cohort approach was used, which included 1,087 cases that were diagnosed during follow-up (2009-2020) and a representative sub-cohort of 4,895 participants. Based on participants’ reported longest-held job, exposure to EDCs of estrogenic (arsenic, BPA, cadmium, copper, PCBs), anti-estrogenic (arsenic, lead, PCBs) and anti-androgenic (arsenic, BPA, lead, phthalates, toluene) mode of action was estimated using the Canadian Job Exposure Matrix. Odds ratios and 95% confidence intervals were estimated separately for the four regional cohorts and then pooled using a random-effects model. Results Compared to those never exposed, participants exposed to BPA (OR=1.70, 95%CI: 1.20-2.41) or 2+ anti-estrogenic EDCs (OR2 EDCs=1.48, 95%CI: 1.09-2.01; OR3 EDCs= OR=17.23, 95%CI: 0.79-375.52) had elevated odds for CRC while an inverse association was observed for cadmium. Substantial heterogeneity was observed across provincial regions. Discussion and conclusion Among EDCs considered, exposure to BPA and multiple anti-estrogenic EDCs in the workplace were associated with elevated risk for CRC. However, conclusions should be tempered given the heterogeneity between the four regional cohorts, low study power for some of the analyses and multiple comparisons.