Despite major advances in childhood cancer treatment, relatively little is known about the causes of these diseases. While genetic factors play an important role, researchers are increasingly investigating the contribution of environmental exposures before birth and during childhood to cancer development. Identifying such factors is particularly important because some exposures may be preventable.
A recent commentary by researchers from the International Agency for Research on Cancer (IARC) Monograph Program and collaborating institutions reviewed current evidence on environmental causes of childhood cancer, highlighting two important developments in 2025. For the first time, IARC identified automotive gasoline and human cytomegalovirus (HCMV) as potential causes of childhood acute lymphoblastic leukemia (ALL) with limited evidence. Previously, parental tobacco smoking was the only factor identified, with limited evidence, for this specific leukemia subtype. For childhood leukemia overall, only x- and gamma-radiation, mixture of fission products, and thorium-232 have been identified as established causes (with sufficient evidence) by the IARC Monographs.
Automotive gasoline contains potentially carcinogenic chemicals, and several studies have reported higher childhood ALL risks associated with parental gasoline exposure or living near gasoline stations. HCMV, on the other hand, is a common virus that can be transmitted from mother to child during pregnancy. Studies examining HCMV maternal serology status or HCMV positivity in stored neonatal blood samples have suggested a possible association between HCMV infection and childhood ALL. These findings are important, yet the possibility of bias or chance cannot be excluded as explanations for the observed associations.
The commentary also discusses how advances in research methods have strengthened the investigation of environmental risk factors. Traditionally, childhood cancer studies often relied on parental interviews to assess past exposures, which can introduce recall bias. Newer approaches include geocoding historical residential addresses and linking them to environmental exposure data, as well as analyzing stored newborn blood samples. Such new methods allow researchers to assess past exposures while reducing reliance on parental recall.
Looking ahead, IARC has prioritized several additional environmental exposures for evaluation between 2025 and 2029, including outdoor air pollution and its components, some pesticides, radon, and parental tobacco smoking. Further studies across different populations, using more precise assessments of specific exposures, are needed to clarify any link and strengthen the evidence for potential causal relationships.
Identifying environmental causes of childhood cancer is particularly challenging given the rarity of these diseases and the potential differences in risk factors across childhood cancer subtypes and exposure periods. Large international collaborations, such as the Childhood Leukemia International Consortium (CLIC), are particularly valuable in overcoming these challenges. By combining data from multiple countries, CLIC enables larger studies and more detailed analyses of specific childhood cancer subtypes and timings of exposure. The IARC commentary acknowledges CLIC’s contribution to the growing evidence on parental smoking as a potential risk factor for childhood leukemia. Continued efforts through collaborations like CLIC may ultimately help identify preventable risk factors and inform future childhood cancer prevention strategies.
Citation:
Article Title: Establishing environmental causes of childhood cancer: a view from the IARC Monographs
Authors: Elisa Pasqual, Andrew Kunzmann, Julia Heck, Margaret R Karagas, Mary K Schubauer-Berigan.
Published In: UCL Open Environ. 2026 Oct 1. DOI: 10.14324/111.444/ucloe.3600.