September is childhood cancer awareness month. The improvement in long-term survival among children with cancer stands among the greatest successes in medicine. However, the incidence of childhood cancer is slowly increasing worldwide. Is there something that can be done to prevent childhood cancer?

It is generally thought that childhood cancers are caused by genetic factors, but not all childhood cancers are caused by genetics. Environmental factors are poorly understood, though researchers are progressively implicating some environmental factors. And some of these environmental factors have been recognized as causes or as potential causes by authoritative bodies, like the Monographs on the Identification of Carcinogenic Hazards to Humans programme of the International Agency for Research on Cancer (IARC), which is part of the World Health Organization (WHO).

How do scientists identify the causes of childhood cancer?

The Monographs programme has evaluated more than 1000 agents to which humans can be exposed in the environment, in the workplace, through diet, or from consumer products. The programme is known as the WHO’s “encyclopaedia of human carcinogens”. For each evaluation, the programme assembles a working group of international experts who are free from conflicts of interest. The working group reviews the scientific evidence on whether an agent can cause cancer in humans (i.e., cancer hazard identification).

Which causes of childhood cancer have been established by the IARC Monographs programme?

In 2025, the programme classified two new potential causes of childhood acute lymphoblastic leukaemia (ALL, the most common type of childhood leukaemia). Two separate working groups found that there was limited evidence that automotive gasoline and human cytomegalovirus (a virus transmitted through body fluids and from mother to foetus during pregnancy) could cause childhood ALL. The evidence was deemed limited because, although there was a credible association in the body of the literature, the association could have arisen due to biases that would need to be clarified with future informative studies.

These two recent evaluations demonstrate how research on the environmental causes of childhood cancer has evolved in recent decades. Using residential data and biological samples collected at birth has allowed researchers to obtain a more reliable measure of exposure, greatly improving studies on childhood cancer.

The IARC Monographs programme has also identified other causes of childhood cancer through its history. Ionizing radiation is an established cause of childhood leukaemia. Parental tobacco smoking causes hepatoblastoma (a common liver tumour in children), and potentially (with limited evidence) childhood leukaemia. There is also limited evidence that benzene can cause childhood acute myeloid leukaemia.

What this article is about and why we chose UCL Open Environment

In this paper, IARC Monographs researchers and collaborators have highlighted the childhood cancer causes categorized by the programme. We also list agents that are currently prioritized for evaluation and have some evidence for a causal role with childhood cancer. For example, air pollution and several components of air pollution have been associated with some types of childhood cancer and are currently prioritized to be evaluated or re-evaluated by the IARC Monographs.

By publishing this paper as open access in UCL Open Environment, we hope to reach researchers, clinicians, policy makers, and members of the public, to raise awareness of the environmental causes of childhood cancer.

Establishing environmental causes of childhood cancer: a view from the IARC Monographs by Elisa Pasqual (IARC, France), Andrew Kunzmann (IARC, France), Julia Heck (University of North Texas, USA), Margaret R Karagas (Dartmouth College, USA), Mary K Schubauer-Berigan (IARC, France) is published in UCL Open Environment volume 8.

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