Abstracts iii35
NEURO-ONCOLOGY • MAY 2017molecular technique in routine praxis, however, with certain technical limits typical for brain tissue and glial tumors. A dual-chromogenic in situ hybridization (CISH) is tested as a possible alternative for FISH in neuropathology. We present the first single institution experience comparing testing of CDKN2A gene changes in parallel by FISH and CISH in a series of 57 patients with grade I-IV glial tumors. In total, 79 samples from 57 patients with astrocytic and oligodendroglial tumors were analyzed. There were 7 gr. I lesions (5 pilocytic astrocytomas, 2 subependymomas), 23 gr. II lesions (12 diffuse astrocytomas, 8 oligodendrogliomas, 1 oligoastrocytoma), 12 gr. III lesions (2 anaplastic astrocytomas, 9 anaplastic oligodendrogliomas, 1 anaplastic oligoastrocytoma) and 37 glioblastomas (gr. IV). Changes of CDKN2A were examined with FISH and CISH technique and evaluated as: no deletion, heterozygous deletion, homozygous deletion and amplification of the gene (found in sporadic cases). Using the ISH technique (finding of the CDKN2A gene change in at least one of the applied method-FISH or CISH -was sufficient for the evaluation of gene status), no CDKN2A changes were found in grade I tumors (0/5). In grade II tumors, homozygous deletion of the gene was found in 38% of cases (39%, 5/12 of astrocytomas and in 25%, 2/8 in oligodendrogliomas). In tumors grade III and IV, CDKN2A gene showed not only deletion (homozygous and heterozygous) but also amplification (4 samples). In total, changes of CDKN2A gene were found in 71% (5/7) of grade III tumors and in 69% (24/35) of grade IV tumors. There were evident differences between oligodendroglioma and astrocytes. However, due to small sample size, no statistical difference could be shown. The concordance of FISH and CISH (after exclusion of specimens with technical limitations) was: 100% in grade I, 70% in grade II, 80% in grade III and 83% in grade IV. In conclusion, this is to the best of our knowledge the first study demonstrating use of CISH for CDKN2A changes in glial tumors. CISH was found as helpful auxiliary molecular method for CDKN2A gene evaluation. INTRODUCTION: The updated 2016 edition of the WHO Classification of Tumor of the Central Nervous System has shifted from the traditional approach primarily based on microscopic features to that on genetic hallmarks. The classification of diffuse gliomas is now defined in accordance with their IDH and 1p/19q status. Although that shift has resulted in a more objective definition of diffuse gliomas, genetic testings, which are not always available worldwide, has become mandatory for WHO diagnosis. Immunohistochemistry (IHC) for mutant IDH1R132H and fluorescence in situ hybridization (FISH) for 1p/19q are the most popular methods, but IDH1R132H does not detect other loci and currently available probes for 1p36 and 19q13 are known to yield false positive results (about 15%). To overcome such disadvantages, we verified the utility of combined IHC for p53 and ATRX in addition to I...
