The epidemiology of infant cancers.

Cancers in infants represent less than 0.05% of all malignant neoplasms, but form a particularly interesting group for study. The ratio of solid tumours to leukaemias is 2:1 in children aged 1-14 but 5:1 in infants less than 1 year. The rate for neuroblastoma which is the most common malignancy in infants is four times higher in children aged under 1 year than in 1-14 year olds. Other embryonal tumours, e.g. Wilms', heptablastoma and retinoblastoma also show higher rates in infants. The ratios of incidence in males to females differed in a number of instances in the two age groups, e.g. in leukaemias and liver tumours the male to female ratio is greater than one in 1-14 year old children but less than one in infants. These observations suggest that many infant tumours may be aetiologically distinct. Their early onset and predominantly embryonal nature suggest a pre-natal origin and genetic factors may be important.