alpha-Internexin expression identifies 1p19q codeleted gliomas

Abstract

Background: alpha-Internexin (INA) is a proneural gene encoding a neurofilament interacting protein that is upregulated in some gliomas, particularly oligodendrogliomas.

Methods: INA expression was evaluated by immunohistochemistry in a series of 122 gliomas, and correlated to the 1p19q codeletion, a favorable prognostic marker of oligodendroglial tumors.

Results: INA expression was strong (>10% positive cells) in 22 cases (22 oligodendroglial tumors and 0 astrocytic tumors), weak (<10% cells) in 14 cases (12 oligodendroglial tumors, 2 glioblastoma with an oligodendroglial component, and 0 astrocytic tumors), and negative in 86 cases (49 oligodendroglial tumors, 9 glioblastoma with an oligodendroglial component, and 28 astrocytic tumors). Among the 27 tumors exhibiting the 1p19q codeletion (all with an oligodendroglial phenotype), INA was detected in 96% (26/27, 18 strong, 8 weak) as compared to 11% (10/95, 4 strong, 6 weak) in the tumors without 1p19q codeletion (with an oligodendroglial or an astrocytic phenotype) (p < 0.001). In oligodendroglial tumors, INA expression specificity for 1p19q codeletion was 86%, sensitivity 96%, positive predictive value 76%, and negative predictive value was 98%. The prognostic impact of INA expression could be evaluated in grade III oligodendroglial tumors. Similar to 1p19q deletion, positive INA expression was correlated with better progression-free survival (52.6 vs 8.7 months [p = 0.001]) and overall survival (121.1 vs 31.4 months [p = 0.0001]).

Conclusion: alpha-Internexin (INA) expression appears to be a simple, reliable prognostic marker and a surrogate marker of 1p19q codeletion.