Not only do children develop cancer, but they can develop cancer at all ages and in all parts of the body from birth onward. Although the causes are not well understood, the vast majority of childhood malignancies develop from immature embryonic tissues. In order of their incidence, they are leukemia, brain tumors, malignant lymphomas and various solid tumors. The common solid tumors are neuroblastoma, nephroblastoma, hepatoblastoma, germ cell tumors, rhabdomyosarcoma, retinoblastoma and osteosarcoma.