c -MYC amplification and expression in astrocytic tumors

The aim of this study was to evaluate the nuclear and cytoplasmic expression of c-MYC protein in human astrocytic tumors of different histopathological grades and to determine whether its expression correlates with c-MYC gene amplification. An immunohistochemical study of c-MYC protein was performed in 140 paraffin-embedded astrocytic tumors of different grades. Among them, 30 specimens were analyzed for c-MYC gene amplification by FISH. Expression of nuclear and cytoplasmic c-MYC was observed, respectively, in 65.0 and 66.4% of the cases studied. The distribution of the positive cases according to the tumor grade increased in both nuclear and cytoplasmic staining with malignancy. The median nuclear LI also increased with tumor grade, with highest c-MYC nuclear expression in grade III. The median cytoplasmic labeling scores showed a significant difference between grade I tumors and diffuse tumors, which presented high and similar median scores. Cytoplasmic c-MYC localization was linked to high nuclear c-MYC expression. FISH results disclosed that the presence of two signals was inversely correlated with histopathological grade, while the presence of ≥5 signals increased according to degree of malignancy. Moreover, the presence of two signals was associated with low nuclear LI and the presence of four or more signals with high nuclear LI. These results indicate that c-MYC expression in astrocytic tumors is strongly associated with increased c-MYC gene copy number and suggest that c-MYC plays a role in the early tumorigenesis of astrocytomas.