[Epidemiology and etiology of childhood hematosarcomas].

Childhood tumours represents the second cause of death in socio-economically developed countries. Ethno-geographical variations in incidence of leukaemias and lymphosarcomas are presented, stressing the contrast between temperate and tropical areas, or between developed and developing countries. Exposure to chemical or biological agents during foetal life and the possible relation with childhood cancers, as well as the role of EBV in Burkitt's Lymphoma, are discussed.