59 Analysis of N-Ras gene mutations in medulloblastomas by polymerase chain reaction and oligonucleotide probes in formalin-fixed, paraffin-embedded tissues

Precise data on the incidence of transforming ras oncogenes in pediatric tumors and the correlations with the histo-pathological properties of the tumor are very limited. Additionally the presence of ras activation in medulloblastomas has not been investigated so far. Using a combination of techiques including specific in vitro gene amplification by polymerase chain reaction (PCR) (Saiki R.K., 1985) and detection of single base mutations by sequence-specific oligonucleotides (SSO) (Farr C.J., 1988) we studied N-ras activation (mutations at codon 12, 13 and 61) in 32 medulloblastomas. DNA was isolated from 5-10 μm sections of formalin-fixed paraffin-embedded tissue (according to Impraim C., 1987). Mutations were found in 3 of 32 examined medulloblastomas. In all cases only mutations of the codon 61 were found : the most frequent was a C-A at position 1 (substitution of a glutamine residue for a lysine). A mutation A-T at position 3 was present in the remaining case. The main advantage of the procedure described are its greatly improved sensitivity, the increased speed by wich tumor samples can be analysed, no longer necessary to use high-M.W DNA and the possibility to use paraffin-embedded sections to analyse various and rare tumors in retrospect.