Background: In 2025, automotive gasoline and human cytomegalovirus (HCMV) were identified as new causes (with limited evidence) of childhood acute lymphoblastic leukaemia by the IARC Monographs programme. Although environmental causes of childhood cancer are generally downplayed over genetic causes, the Monographs programme, throughout its history, has identified few other causes for specific childhood cancers and new potential environmental causes of childhood cancer are increasingly being reported in the epidemiological literature.
Objectives: Here, we review childhood cancer causes evaluated by the IARC Monographs, with a more detailed description of the evaluation for automotive gasoline and HCMV, reflecting on how childhood cancer etiological research has evolved. We will also list agents currently prioritized for an IARC Monographs evaluation in the 2025-2029 period that were associated with increased risk of childhood cancer in epidemiological studies. 
Methods: The IARC Monographs programme maintains the list of classified agents continuously updated and freely accessible on its website. We extracted data from this list. Information on prioritized agents for 2025-2029 was extracted from the report of the IARC Advisory Group, which met in Lyon in March 2024 to prioritize dozens of nominated agents.
Results: Childhood cancer is a rare outcome; hence, it is efficiently studied in case-control studies. However, with this design, exposure data have been traditionally collected by questionnaire at the time of diagnosis. In recent decades, childhood cancer case-control studies have improved by progressively including assessment of exposure prior to diagnosis (e.g. use of geocoding methodology or stored neonatal bloodspots), and these methodologies were instrumental in the automotive gasoline and HCMV IARC Monographs evaluations.
Among the nearly 200 agents currently prioritized for IARC Monographs evaluation (2025-2029), several have been sporadically linked to increased childhood cancer. For example, positive associations for specific childhood cancer subtypes were reported for parental cannabis smoking in case-control studies in the 1990s and early 2000. An IARC Monographs evaluation of cannabis smoking is planned for November 2026.
Conclusions: Environmental causes of childhood cancer are progressively being identified due to improvements in epidemiological studies and are increasingly being recognized by the scientific community, as reflected in recent Monographs classifications.