Molecular Analysis of Tumor Cell Components in Pilocytic Astrocytomas, Gangliogliomas, and Oligodendrogliomas

Gliomas and glioneuronal tumors are histologically polymorphous tumors. They can harbor a clear cell "oligodendroglial-like" component that can be difficult to distinguish from tumor cells of oligodendrogliomas or neurons, particularly on small samples. Thus, knowledge of the pattern of molecular markers in different tumor cell components is essential to ensure reliable diagnosis. Here, we screened 14 pilocytic astrocytomas (PA), 12 gangliogliomas, and 13 oligodendrogliomas for the KIAA1549-BRAF fusion gene, IDH1/2 mutations, and 1p19q losses in various areas of interest representative of the different tumor cell components. Molecular patterns were analyzed according to histologic type, tumor cell components, and clinical data. The KIAA1549-BRAF fusion gene was detected only in 8 out of 11 PAs (73%) and in 3 out of 9 gangliogliomas (33%) (P=0.003). Interestingly, all of the studied areas of interest within the same tumor exhibited the same KIAA1549-BRAF fusion gene status. IDH1-R132H and 1p19q loss were found only in 12 out of the 13 oligodendrogliomas (P<0.0001). Our study shows that cellular polymorphism in PAs and gangliogliomas does not affect the results of molecular analysis investigating the status of the KIAA1549-BRAF fusion gene. Thus, this molecular analysis can be reliably used even if the sample size is limited and the selection of different tumor areas is not possible.