[1493] Comparision of EGFR Immunohistochemistry of wt-EGFR with EGFRvIII and Correlation with EGFR Gene Amplification in Glioblastoma Multiforme

G Gupta, LR Sharer, ES Cho, MR Hameed. University of Medicine and Dentistry of New Jersey, Newark, NJ

Background: Glioblastoma multiforme (GBM) is the most common and most malignant of glial tumors. Many studies have shown the presence of molecular genetic alterations in GBM, the most frequent of which is Epidermal growth factor receptor (EGFR) gene amplification. This leads to an overexpression of EGFR protein. Majority of GBMs with this amplification show a variety of qualitative EGFR alterations, resulting in different EGFR mutations. The most common EGFR mutation is EGFRvIII (deletion of exons 2-7) which presumably occurs through alternative splicing or gene rearrangements. Unlike wild type(wt) EGFR, EGFRvIII has a truncated extracellular ligand-binding domain which lends it a ligand-independent constituitive activity and enhanced tumorigenecity. EGFR amplification is a very strong indicator of poor survival prognosis. We have studied the expression of wt and mutated EGFRvIII and correlated the findings with gene amplification in a group of patients with GBM.
Design: Twenty three cases of Glioblastoma multiforme were selected, of which twelve were males and eleven were females, ages (20 to 84). We analysed the protein expression of wtEGFR, EGFR deletion mutant variant III (EGVRvIII) and performed gene amplification for EGFR. After histology review, 5 micron thin sections were cut from formalin fixed paraffin embedded tissue blocks and specific monoclonal antibodies for EGFR, EGFRvIII were used for immunohistochmical detection of the same. We then used fluorescent in situ hybridization (FISH) to assess the EGFR gene amplification in these cases. The cases that were positive for EGFRvIII expression were selected and a dual probe FISH assay was performed on paraffin embedded sections with locus specific probes for EGFR and the centromere of chromosome 7 (CEP 7).
Results: Of the 23 patients of glioblastoma, eleven (47.3%) expressed EGFRvIII and nine (39.1%) expressed EGFR. When they were analysed for gene amplification by FISH, of the eleven patients that expressed EGFRvIII, six (54.5%) showed high amplification, three (27.2%) showed extra chromosomes and two (18.1%) were normal.
Conclusions: 1) EGFR over-expression is a common finding in Glioblastoma Multiforme. 2) Gene amplification is seen in about half of the cases with EGFRvIII expression. 3) High level amplification was seen in cases with positive wild type and mutant proteins. 4) Immunohistochemical analysis of wild type EGFR alone may not be sufficient to determine EGFR status in GBM.
Category: Neuropathology

Monday, March 9, 2009 2:15 PM

Platform Session: Section H, Monday Afternoon