Abstract
Background: Causes of childhood cancer remain poorly understood. Using data from the case-control studies of the Childhood Cancer and Leukemia International Consortium (CLIC), we explored how maternal education as a key socioeconomic status (SES) indicator, varies across studies/countries and contributes to understanding of potential environmental and lifestyle risk factors.
Methods: Control group data from cancer-free children matched by diagnosis date of cases from 16 studies were included, using both interview-based and health registry sources. Maternal education, the primary SES measure used in previous analyses with pooled CLIC data, was categorized as low, medium, or high according to the International Standard Classification of Education. Multinomial logistic regression assessed associations between maternal education and perinatal/lifestyle factors, calculating crude and adjusted odds ratios (ORs) and 95 % confidence intervals (CIs) for high vs. low education.
Results: Maternal education levels varied across studies and over time, with the highest proportions of highly educated mothers in the U.S. and lowest in Costa Rica, Italy, and Egypt. Higher maternal education was generally positively associated with higher birthweight, breastfeeding, daycare attendance, and maternal prenatal alcohol consumption. Higher maternal education was generally inversely associated with lower birthweight, younger maternal age, paternal occupational pesticide exposure, maternal prenatal smoking, and having more siblings. The direction of associations for older maternal age and for caesarean delivery differed substantially across regions. Exclusion of mothers < 21 years at birth of the index child had little effect on the results.
Conclusion: This multi-country analysis supports the use of maternal education for adjustment as a proxy for SES, showing largely consistent associations with various behaviors and exposures. While the direction of associations was generally consistent, the strengths varied sometimes considerably by geographical region. These findings support the inclusion of maternal education as a covariate in analyses of childhood cancer risk when pooling CLIC studies.