Test Details: Glioblastoma is known to be the most malignant of the glial tumours. A minor fraction of glioblastoma may contain areas showing oligodendroglioma-like tumour cell differentiation. The oligodendroglial component and combined loss of chromosomal arm 1p and 19q in glioblastoma indicate increased survival. 1p and 19q deletion by fluorescence in situ hybridization (FISH) is designed to detect loss of chromosome loci 1p and 19q, which has been seen in oligodendroglial tumours and which has been associated with improved prognosis and response to therapy in patients with primary brain tumours.