BACKGROUND: Acute leukemia is the most common cancer in children under 15 years of age; 80% are acute lymphoblastic leukemia (ALL) and 17% are acute myeloid leukemia (AML). Childhood leukemia shows further diversity based on cytogenetic and molecular characteristics, which may relate to distinct etiologies. Case-control studies conducted worldwide, particularly of ALL, have collected a wealth of data on potential risk factors and in some studies, biospecimens. There is growing evidence for the role of infectious/immunologic factors, fetal growth, and several environmental factors in the etiology of childhood ALL. The risk of childhood leukemia, like other complex diseases, is likely to be influenced both by independent and interactive effects of genes and environmental exposures. While some studies have analyzed the role of genetic variants, few have been sufficiently powered to investigate gene-environment interactions. OBJECTIVES: The Childhood Leukemia International Consortium (CLIC) was established in 2007 to promote investigations of rarer exposures, gene-environment interactions and subtype-specific associations through the pooling of data from independent studies. METHODS: By September 2012, CLIC included 22 studies (recruitment period: 1962-present) from 12 countries, totaling approximately 31000 cases and 50000 controls. Of these, 19 case-control studies have collected detailed epidemiologic data, and DNA samples have been collected from children and child-parent trios in 15 and 13 of these studies, respectively. Two registry-based studies and one study comprising hospital records routinely obtained at birth and/or diagnosis have limited interview data or biospecimens. CONCLUSIONS: CLIC provides a unique opportunity to fill gaps in knowledge about the role of environmental and genetic risk factors, critical windows of exposure, the effects of gene-environment interactions and associations among specific leukemia subtypes in different ethnic groups. ; Metayer, Catherine Milne, Elizabeth Clavel, Jacqueline Infante-Rivard, Claire Petridou, Eleni Taylor, Malcolm Schuz, Joachim Spector, Logan G Dockerty, John D Magnani, Corrado Pombo-de-Oliveira, Maria S Sinnett, Daniel Murphy, Michael Roman, Eve Monge, Patricia Ezzat, Sameera Mueller, Beth A Scheurer, Michael E Armstrong, Bruce K Birch, Jill Kaatsch, Peter Koifman, Sergio Lightfoot, Tracy Bhatti, Parveen Bondy, Melissa L Rudant, Jeremie O'Neill, Kate Miligi, Lucia Dessypris, Nick Kang, Alice Y Buffler, Patricia A 1R13ES022868-01/ES/NIEHS NIH HHS/United States P01 ES018172/ES/NIEHS NIH HHS/United States R03 CA132172/CA/NCI NIH HHS/United States R03CA132172/CA/NCI NIH HHS/United States R13 ES021145/ES/NIEHS NIH HHS/United States R13 ES021145-01/ES/NIEHS NIH HHS/United States Canadian Institutes of Health Research/Canada Department of Health/United Kingdom Research Support, N.I.H., Extramural Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. Netherlands Cancer epidemiology Nihms434934 Cancer Epidemiol. 2013 Jun;37(3):336-47. doi: 10.1016/j.canep.2012.12.011. Epub 2013 Feb 9.