Expression of O 6 -methylguanine-DNA methyltransferase in childhood medulloblastoma Denis FaoroAndreO. von BuerenTarek ShalabyDavide Sciuscio • Marie-Louise HurlimannLucia ArnoldNicolas U. GerberJohannes Haybaeck • Michel MittelbronnStefan RutkowskiMonika HegiMichael A. Grotzer