In France, around 2,260 new cases of cancer are diagnosed each year in children under the age of 18. Leukaemia accounts for around 26 per cent of cases, central nervous system tumours for 25 per cent and lymphomas for 15 per cent. Paediatric cancer therefore remains a rare disease.
However, a study published by Santé publique France in September 2026 reveals a new development. Between 2000 and 2020, the incidence of central nervous system tumours in children under the age of 15 increased by an average of 0.93 per cent per year. But the researchers are quick to point out that a significant proportion of this increase can be attributed to improved diagnosis, increased monitoring of certain at-risk populations and changes in tumour classification. In other words, we are now detecting cancers that might not have been as accurately identified or classified twenty years ago.
So, what causes cancer in a child? This is precisely one of the great mysteries of oncology. Unlike cancers in adults, it is rarely possible to link them to smoking, alcohol, diet or decades of occupational exposure. According to the World Health Organisation, the cause of the majority of childhood cancers remains unknown. Around 8 to 10 per cent are thought to be linked to a hereditary genetic predisposition.
Many paediatric cancers begin with genetic abnormalities that arise spontaneously during a child’s development, sometimes even before birth. A cell acquires a genetic mutation, after which further abnormalities may occur, leading to its uncontrolled proliferation. We should therefore not automatically look for an identifiable external cause.
Environmental factors are, however, being studied very closely. One of the few factors that are indisputably carcinogenic in children is significant exposure to ionising radiation. Children are, in fact, more sensitive to radiation than adults. Some studies have also observed an increased risk following relatively high doses of medical radiation, which is why CT scans and other radiological examinations are now used with greater caution in paediatrics.
Pesticides are also among the avenues being investigated, particularly in relation to leukaemia. The International Agency for Research on Cancer has identified evidence linking certain occupational exposures to pesticides among parents. However, these associations do not yet allow us to conclude that pesticides are responsible for an overall increase in childhood leukaemia. Many other environmental factors have been investigated, but no single major cause has yet been identified.
Certain infections also play a role in specific cancers. The Epstein-Barr virus, HIV or, in certain parts of the world, malaria are associated with an increased risk of certain childhood cancers. Here too, they account for only a fraction of cases.
Finally, there is a statistical phenomenon that should not be underestimated: we are better at screening. Imaging techniques are more advanced, molecular genetics allows us to characterise tumours that were previously difficult to identify, and national registries are recording cancers with increasing accuracy. An increase in the number of diagnoses therefore does not automatically mean that more children are actually developing cancer.
This does not mean that there are no as yet unknown environmental effects. On the contrary. The extremely young age of some patients suggests that events occurring during pregnancy, the first years of life, or even in the parents’ germ cells could play a role in certain cancers. This is why researchers are investigating, in particular, parental occupational exposures, pollutants, pesticides, radiation, infections and immune mechanisms. However, for the time being, none of these lines of inquiry alone can explain a supposed general rise in cases.
Globally, more than 275,000 cases of cancer were diagnosed in 2024 among those under the age of 20, according to the International Agency for Research on Cancer, and the actual figure could be higher due to under-diagnosis in many countries.
Herein lies the paradox: whilst modern medicine is now remarkably effective at treating many childhood cancers – with a cure rate of over 80 per cent in countries with well-developed healthcare systems – it still does not know why the majority of these cancers develop.
Perhaps the most accurate scientific question is therefore not yet ‘why are children developing more and more cancers? ’, but rather: to what extent does the observed increase correspond to a genuine rise in risk, to what extent is it due to improved diagnosis, and what environmental or biological factors are still beyond our understanding?*
This is precisely what research must now determine.
