| Popis: |
Under 2% of all cancers in industrialized countries occur in childhood and adolescence, but they account for a much larger proportion of total population life years potentially lost to cancer. Total incidence is about 160 per million in children and 200 per million in adolescents. In children, leukaemias account for one third of all malignancies and CNS tumours for one quarter. In adolescents, lymphomas account for one quarter of cases and leukaemias, CNS tumours, and carcinomas each for about 15%. Five-year survival exceeds 80% for many childhood and some adolescent cancers. Although survival of adolescents is high overall, survival for several types of cancer is markedly lower than in children. Infants under a year of age also tend to have lower survival. Excess mortality continues beyond 25 years from diagnosis of childhood cancer. The risk of developing a second primary cancer is about six times that in the general population. The causes of most childhood cancers remain unknown. The principal established exogenous causes are ionizing radiation, ultraviolet radiation from sunlight, and certain viruses. Up to 10% of children and adolescents with cancer may have germline mutations in cancer predisposition genes. If one child in a family has cancer, then that child’s siblings have approximately double the risk of the general population for developing childhood cancer, but this could well be entirely accounted for by familial syndromes. Significantly raised or reduced risks of childhood cancers have been linked to polymorphic variants of certain genes, though many of these associations remain to be replicated. |
