Central nervous system tumours in children: epidemiology and risk factors.

In children, a variety of distinct tumour types arise in the central nervous system (CNS) but they are frequently considered by epidemiologists as a single entity. CNS tumours are the second most common childhood malignancy and occur more frequently in developed countries than developing nations. Approximately 50% of paediatric CNS tumours are gliomas, with astrocytomas of the piloctyic type predominating. Distributions of subtypes by age show that primitive neuroectodermal tumours (PNET) and ependymomas mainly occur in children less than 10 years. There is an ongoing debate with regard to the apparent increases in incidence over recent decades, which, it has been suggested, are accounted for by improved diagnostic technologies implemented in the mid 1980s. CNS tumours differ between children and adults with respect to the proportion of all cancers (20% in children, less than 2% in adults), their cellular origins, classification scheme, the proportions of pathological subtypes, and anatomic site. The causes of childhood CNS tumours are largely unknown; and although an estimated 5% or more may be explained by genetic predisposition, investigations of environmental aetiology have not been fruitful. Whilst high dose ionising radiation is an established risk factor for this group of tumours, reported associations with dietary N-nitroso compounds have not been consistent. Exposure to ELF EMF, at any level, has not been associated with childhood CNS tumours, but the current evidence base is inadequate for complete evaluation. The rarity of childhood CNS tumours necessitates careful attention being paid to the design of future aetiological studies.