Epidemiological investigations on neuroblastomas in Denmark 1943-1980.

During the period 1943-1980 a significant increase in the incidence of neuroblastoma was seen in Denmark. The incidence increased from a level corresponding to that in Finland to a level corresponding to that in the USA, and the increase appears to be continuing. The increase relates to children aged under 5 years, and is most pronounced in infants under 1 year. The incidence in the first year of life has, however, not yet reached the level of the USA. The increase in incidence is most likely a result of improved diagnosis, changes in the social composition of the population, and an increase in environmental carcinogens of importance in the induction of neuroblastomas. The incidence is lower in children of self-employed parents, and higher in infants of mothers aged under 20 or over 34 years. Aside from lower socio-economic circumstances for mothers under 20 years, no specific risk factors were revealed in this study. The observations of a family in which the mother has ganglioneuroma and both daughters have developed neuroblastoma, of a child who suffered from both neuroblastoma and neurofibromatosis von Recklinghausen, and of a significantly higher frequency of infants with signs of multicentric tumours in the offspring of mothers aged under 20 and over 34 years of age, is consistent with the two-hit theory of Knudson et al. (1972).