Ras oncogene mutations in childhood brain tumors.

Although N-nitroso compounds (NNC) are ubiquitous in the human environment and are known neurocarcinogens in animal models, results of epidemiological studies have not yet convincingly associated NNCs with brain tumor occurrence in humans. Animal studies have suggested that specific codons (12, 13, and 61) in the ras family are mutable by exposure to NNCs. The purpose of this study was to measure the presence of mutations in the ras family of oncogenes in tissue from childhood brain (CB) tumors as a preliminary step toward investigating their potential use as biomarkers of chemical exposure. DNA was extracted from paraffin-embedded formalin-fixed CB tumors from tissues resected during neurosurgical operations. Using the PCR, designed RFLP-screening methods, and sequencing, we attempted to screen brain tumors from 46 children for the presence of H, K, and N-ras mutations at codons 12, 13, and 61. Screening for oncogene mutations using PCR, RFLP methods, and DNA sequencing was successfully completed for a high proportion of the available specimens. Astrocytoma specimens from three children for whom screening with PCR was successfully completed were found to contain CAA-->GAA point mutations in K-ras at codon 61. None of the specimens contained mutations at any of the other locations. These results, although preliminary, provide a potential clue for future mechanistic studies of CB tumors. The possible roles of NNCs in inducing this mutation, or of this mutation as an early or late event in tumor progression, however, remain unclear.