Department of Laboratory Medicine, CORE Diagnostics, Gurgaon, India Does Molecular Profile Trump Morphology in Glial Neoplasms: An Indian perspective, based on the Current WHO Classification (2016) Shivani Sharma, Sambit K. Mohanty, Arbind Singh, Anurag Sharma, Bekleshwar Salona, Mukesh Kumar, Mohit Kumar, Santosh Pandey, Rahul Katara, Sankar Mohan, Vipin Kumar, Joydeep Mukherjee, Ajay Pandita, Lata Kini Department of Laboratory Medicine, CORE Diagnostics, Gurgaon, India Introduction: Gliomas are the most common and a heterogeneous group of primary tumors of the central nervous system. Histomorphology has been the mainstay in the diagnosis of gliomas till it was realized that alone it lacks the precision that is needed for tailored treatment of individual patients. With accumulating data and evidences on these molecular signatures, it has been realized that an integrated phenotypic and genotypic approach defines these group of tumors. The 2007 World Health Organization (WHO) classification was based on the concept of histogenesis where in the characterization of these tumors was based on histomorphology, ultrastructural features, and lineage associated immunohistochemical markers. WHO classification system for 2016 reflects a major paradigm shift in the diagnosis and nomenclature of glial tumors to improve the management of the patient by yielding biologically homogenous and narrowly defined entities. Results: Figure 1: Percentage distribution of cases according to WHO 2007 classification. Figure 2: Percentage distribution of cases according to WHO 2016 classification Figure 3: Categories of glial neoplasms and their comparison per WHO, 2007 and WHO, 2016 Aim: We revisited and applied the current WHO guidelines in 151 glial neoplasms to evaluate and understand its utility. 1p32 1q42 19p13 19q13 Materials and Methods: This is a retrospective study that includes 151 glial neoplasms H&E slides were reviewed per the 2007 WHO classification. A review of 1p/19q co-deletion and IDH mutation status was done and the results were compiled to assign the new nomenclature according to the latest 2016 WHO CNS tumor classification system. FISH assay was performed on FFPE tissue sections following tumor area selection. FISH assay was then performed in three basic steps namely, pre-treatment of the slides, co-denaturation, and hybridization of FISH probes and slides, and post-hybridization washing. Dual color probe signals were assessed keeping green (CEP17) signals as the internal control. A tumor was considered to have 1p deletion when the 1p probe to 1q probe ratio (1p/1q) ratio was <0.80 and was considered to have 19q deletion when the 19q probe to 19p probe ratio (19q/19p) was <0.80. DNA was extracted from the representative tumor block and polymerase chain reaction with sequencing was performed. The PCR product sequence was then aligned with the wild type sequence to detect the codons (hot spot region) of interest. Figure 4: Oligodendroglioma (H&E, 400x). Figure 5: IDH1 mutation on exon4, PCR with sequencing Figure 6: 1p and 19q deletion of oligodendroglioma tumor cell nuclei (FISH; 60x) Conclusions: Diffuse astrocytoma, mutant type outnumbered the wild type. Diffuse gliomas, IDH wild type are an uncommon diagnosis and need further careful evaluation to completely exclude other low-grade lesions such as gangliogliomas. Demonstration of both IDH gene mutation and 1p/19q whole arm co-deletion is mandatory to define oligodendroglial neoplasms. Three cases of diffuse glioma and one of anaplastic astrocytoma were merged to the oligodendroglial group after correlation with characteristic molecular signatures (IDH1 mutation and 1p/19q co-deletion). Vice versa, four cases that were morphologically diagnosed as oligodendrogliomas were termed as diffuse astrocytoma IDH wild type (n=2), and IDH mutant (n=2) on molecular correlation. This transition highlights that the molecular classification trumps over morphology in brain tumors. 60% tumors of oligoastrocytic group could be categorized as pure oligodendroglial or astrocytic after molecular evaluation. GBM(O) category has been eliminated that comprised of 5% cases of the tumors in the present study. Our study emphasizes the utility of molecular analysis in the classification of the glial neoplasms as pure oligodendroglial or astrocytic in nature, validating and reiterating the new WHO classification.