Parental exposure and risk factors for leukemia in offspring. A systematic review

Objective: The purpose of this thesis is to identify and investigate risk factors associated with childhood leukemia, formulated by the research question: Which risk factors are associated with parental exposure and childhood leukemia in the offspring? Methods: A systematic literature search was performed in three databases Embase, Medline and Cochrane. The articles found were selected and included when related to the research question. All articles were evaluated for risk of bias and level of evidence using the quality assessment system Grading of Recommendation, Assessment, Development and Evaluation (GRADE). The exposures were divided into several categories, all relevant to parental exposure: air pollution, use of alcohol and medications, occupational exposure, pesticides, socio-economic status (SES) and smoking. Results/Discussion: 27 articles were found and included in the systematic review. Exposure to petroleum and hydrocarbons as well as pesticides appears to increase the risk of childhood leukemia. A high risk of bias was found in several of the studies and GRADE level varied from very low to medium with no studies in the high category. Heterogeneity was high between the studies, both in way of exposure measurement and in exposure category. The lack of differentiation in the outcome between different subtypes of leukemia in childhood was problematic and new research must consider this. Conclusion: There is not enough evidence to support that smoking, use of alcohol or medications and SES are risk factors for childhood leukemia. What we can determine is that pesticides, solvents and petroleum-derivates can be considered as potential risk factors and that timing of exposure is crucial for the development of childhood cancer. However, we cannot conclude that there is any causality between the risk factors and childhood leukemia, nor any of its subtypes. Register-based cohorts with global cooperation, with focus on subgroups, should be performed to better understand the impact of parental exposure and risk of childhood leukemia