Molecular Biology of Pediatric Brain Tumors

OBJECTIVES:

• Determine the chromosomal gains and losses by DNA ploidy analysis and comparative genomic hybridization in patients with primitive neuroectodermal tumors or medulloblastomas.
• Determine the frequency of specific chromosomal abnormalities, including deletions of chromosomal regions 6, 17, and 22, in these patients.
• Perform a statistical analysis to determine possible associations of chromosomal abnormalities and DNA ploidy with patient age, tumor histology, tumor location, extent of disease, and event-free survival.

OUTLINE: DNA ploidy analysis will be performed to determine the overall level of aneuploidy. The results are compared to the comparative genomic hybridization (CGH) analysis, which is used to demonstrate tumor-specific losses or gains, including amplification, of specific chromosomal regions. Tumors are also screened for specific abnormalities by fluorescent in situ hybridization (FISH), which detects chromosomal rearrangements, including balanced translocations, deletions, amplifications, etc. PCR-based microsatellite polymorphism analysis may also be performed.

Primitive neuroectodermal tumors (PNETs) are screened by FISH with a distal 17p13.3 cosmid and a 17q25 cosmid to identify tumors with a 17p deletion. Atypical teratoid/rhabdoid tumors and PNETs without a 17p deletion are screened by FISH with a series of cosmids from 22q11.2. PNETs are also screened by interphase FISH with cosmids from chromosome 6 to identify tumors with deletions.

Patients do not receive the results of the genetic testing and the results do not influence the type or duration of treatment.