Background:
Persistent organic pollutants (POPs) are endocrine-disrupting industrial chemicals that accumulate in fat tissues and have been shown to be associated with adverse health effects, such as obesity and obesity-related diseases. To date, findings on association between POPs and hormone-sensitive obesity-related cancers are conflicting, and only few studies have investigated the potential interaction between POPs and adiposity.
Objectives:
This project aims at evaluating the current evidence on the association between POP levels and the risk of female cancers (breast, endometrial, ovarian), prostate and colorectal cancer, accounting for body fatness.
Methods:
A systematic literature review was conducted in PubMed, Scopus and Web of Science. Meta-analysis of mean differences and risk estimates were performed using random-effects models. Heterogeneity was assessed using the I2-statistic and the final quality of evidence was determined using the GRADE framework.
Results:
A total of 22, 4, 3, 13 or 7 publications were included on POPs and breast, endometrial, ovarian, prostate or colorectal cancer, respectively. No significant mean differences between cases and controls were observed for breast (p,p´-dichlorodiphenyldichloroethylene (p,p´-DDE), total PCBs), endometrial (β-HCH, HCB, Oxychlordane, p,p´-DDE, p,p´- dichlorodiphenyltrichloroethane (p,p´-DDT), trans-nonachlor), ovarian (α-HCH, β-HCH, γ-HCH, Heptachlor), prostate (α-HCH, β-HCH, HCB, Mirex, oxychlordane, p,p´-DDE, p,p´-DDD, p,p´-DDT, trans-nonachlor, and PCB congeners 118, 138, 153, 156 and 180) and colorectal cancer (α-HCH, β-HCH, heptachlor epoxide, o,p´-DDE, o,p´-DDT, p,p´-DDE, p,p´-DDT, trans-nonachlor, and PCB congeners 52, 101, 105, 118).
A significant positive association between higher concentrations of p,p´-DDT (OR unadjusted for BMI: 1.80, 95%CI 1.08-3.00, , I2 0.0%, n study=2) and endometrial cancer risk was found. Stratification was not possible for BMI. Additionally, we observed a significant positive association between heptachlor epoxide and prostate cancer (OR 1.70, 95%CI 1.01-2.86, I2 0.0%, n study=3), which was attenuated after adjusting for BMI (OR 0.81, 95%CI 0.15-4.54, I2 79.8%, n study=2).  Stratification by BMI was only available for breast cancer and the analysis is ongoing.  
Conclusions/Implications:
Results from this systematic review and meta-analysis pinpoint the current gap in knowledge. Even though slight associations between POPs and cancer risk have been observed, the heterogeneity and the paucity of studies hamper firm conclusion. Additionally, further research is needed to clarify the role of body fatness in the association between POPs and hormone-sensitive obesity-related cancers.