Cancer epidemiology and environmental factors in children, adolescents and young adults

Introduction Cancer is a rare disease in childhood. In developed countries, only about 0.5% of all cases occur in children under 15 years of age. The incidence rates range between 96 and 138/million children per year for males and between 70 and 116/million children for females [1]. Contrary to what is observed in adults, epithelial cancers (carcinomas) are rare among children, and in this age group solid tumors are predominantly embryonal. Therefore, it is more appropriate to classify childhood cancers according to their histology. According to the International Classification of Childhood Cancer [2], childhood tumors are classified into 12 major diagnostic groups: leukemias, lymphomas, central nervous system (CNS) tumors, sympathetic nervous system tumors, retinoblastomas, renal tumors, liver tumors, bone tumors, soft tissue sarcomas, germ cell tumors, epithelial tumors and other and unspecified malignant cancers (Table 8.1 [2]). Leukemias, brain tumors and non-Hodgkin's lymphomas (NHLs) are the most frequent pediatric cancers in developed countries, representing almost 60% of all cases, while in developing countries NHLs are more common than brain tumors (Figure 8.1) [3]. Each year, an estimated 160 000 cancers are diagnosed in children worldwide, and an additional 240 000 cancers in adolescents and young adults (aged 15–24 years) [1].