In Europe 1 child in 600 develops cancer before the age of 15. Annual incidence 1:10,000; ~1200 new cases/year in UK. Pattern of childhood cancers is very different from that seen in adults: carcinomas are rarely seen. Overall, childhood cancer is slightly more common in boys than girls.

• Leukaemias account for about 35% of the total: 80% are some type of ALL, 15% some type of AML. 5% chronic myeloid leukaemias, (adult and juvenile types) or myelodysplastic syndromes. CLL does not occur in children.

• Brain tumours are commonest solid malignancies, 25% of the total. Different tumour types from adults; commonest medulloblastoma in posterior fossa.

• Embryonal tumours 15%, seen almost exclusively in children. Include neuroblastoma, nephroblastoma (Wilms' tumour), rhabdomyosarcoma, hepatoblastoma.

• Bone tumours 5% osteosarcoma, Ewing's sarcoma.

• Lymphomas 9%—NHL and Hodgkin's disease. NHL in children closely related biologically to ALL; low grade disease very rare.

• Remainder of cases are mainly germ cell and primitive neuroectodermal tumours (PNETs), including retinoblastomas.

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