In terms of its molecular biology and molecular genetics,
medulloblastoma is the most thoroughly studied of the pediatric
brain tumors. Alterations in chromosome 17, usually an
isochromosome 17q, are the most common
cytogenetic abnormalities. Similarly, deletion of the short arm of one 17 chromosome, the result of formation of an iso17q, is the most common molecular
biological abnormality found. The gene or genes important in the development of
medulloblastoma found on chromsome 17 have not yet been identified. Both a tumor suppressor gene and an oncogene have been identified that may play a role in the development of this
tumor type. The Patched (PTC) tumor suppressor gene is inactivated in approximately 15% of medulloblatomas; this alteration may be specific to the desmoplastic variant. Oncogenic mutations in the
beta-catenin gene are found in a small subset of
medulloblastomas. Both of these genes play central roles in developmental pathways. Prognosis in this
tumor type has been related to the level of expression of the
neurotrophin receptor trkC. In this review, these and other molecular
biological and genetic findings are discussed with respect to the development of
medulloblastoma.