Medulloblastoma (WHO grade IV) is a malignant, invasive embryonal tumor of the cerebellum that occurs primarily in children, has a predominantly neuronal differentiation, and has a tendency to metastasize via CSF pathways. The annual incidence is 0.5 per 100,000 children younger than 15 years. In adulthood, 80% of medulloblastomas occur in people aged 21 to 40 years. These types of tumors rarely occur beyond the fifth decade of life. Medulloblastomas have been diagnosed in several familial cancer syndromes, including TP53 germline mutations, the nevoid basal cell carcinoma syndrome (NBCCS), and Turcot syndrome type 2. The most common specific cytogenetic abnormality in medulloblastomas is isochromosome 17q [i(17q)], which is present in approximately 50% of cases. A number of genetic alterations in this tumor have been described, but none appear to be specific for this tumor. The 5-year survival rate has been estimated to be 50% to 70%. The incidence in adults is 0.05 per 100,000. Medulloblastoma responds to surgery, radiation therapy, and chemotherapy.
Supratentorial primitive neuroectodermal tumor (PNET) (WHO grade IV) is an embryonal tumor in the cerebrum or suprasellar region that is composed of undifferentiated or poorly differentiated neuroepithelial cells, which have the capacity for differentiation along neuronal, astrocytic, ependymal, muscular, or melanocytic lines. Synonyms include cerebral medulloblastoma, cerebral neuroblastoma, cerebral ganglioneuroblastoma, blue tumor, and primitive neuroectodermal tumor. This is a rare tumor that occurs in children (mean age, 5.5 years); a precise incidence has not been determined. No specific cytogenetic abnormalities or molecular genetics exist with this tumor. The overall 5-year survival rate has been reported to be 34%.
(Refer to the Embryonal Cell Tumors section of this summary for treatment information. Refer to the PDQ summary on Childhood Central Nervous System Embryonal Tumors Treatment for more information.)
Choroid plexus tumors
Choroid plexus papilloma (WHO grade I) and choroid plexus carcinoma (WHO grade III) are intraventricular papillary neoplasms derived from choroid plexus epithelium. These types of tumors account for 0.4% to 0.6% of all brain tumors, 2% to 4% of brain tumors in children, and 10% to 20% of brain tumors manifesting in the first year of life. Papillomas outnumber carcinomas by a 10:1 ratio. Lateral ventricle tumors occur primarily in children; fourth ventricle tumors are evenly distributed among all age groups. An association between infection with simian virus 40 (SV40) and choroid plexus tumors has been made. These types of tumors occasionally occur in patients with Li-Fraumeni syndrome. No specific cytogenetics or molecular genetics exist with these types of tumors. Choroid plexus papilloma can be cured surgically and has a 5-year survival rate of as much as 100%. Choroid plexus carcinomas have a less favorable outcome and a 5-year survival rate of 40%.