Embryonal Tumors

Abstract

Embryonal tumors of the central nervous system (CNS) are the most common group of malignant brain tumors in childhood. Diagnosis and classification of these tumors got refined repeatedly over the last decade, due to ongoing improvements in molecular genetics. These tumors account for 20% of all childhood CNS tumors and mainly include medulloblastomas, atypical teratoid/rhabdoid tumors (AT/RTs), and CNS primitive neuroectodermal tumors (CNS-PNETs). Rare histopathological variants are embryonal tumor with multilayered rosette, medulloepithelioma, CNS neuroblastoma, CNS ganglioneuroblastoma, CNS embryonal tumor not otherwise specified (NOS), and CNS embryonal tumor with rhabdoid features. The incidence rate is 10.2–11.6 per million per year from infancy to the age of 3 years. With increasing age the incidence gradually declines. In adults, these tumors are extremely rare. The outcome for patients with tumors diagnosed as embryonal CNS tumors is generally poor and is associated with a high mortality and a significant long-term morbidity. Particularly in infants, in metastatic medulloblastomas or in any high-risk embryonal CNS tumors, the outcome remains poor even when aggressive therapies are applied. Current treatment approaches include surgery, chemotherapy (CTx), and radiotherapy (RT). RT fields typically cover the full craniospinal volume followed by a local boost to the tumor bed. For children younger than 3 years of age, attempts have been made to minimize neurotoxic effects by delaying or even avoiding RT altogether and by applying intensified CTx regimens instead. In the future, refining risk stratification by molecular genetics may enable treatment optimization and the development of individualized targeted therapies.