Predominant Expression of Mutant EGFR (EGFRvIII) is Rare in Primary Glioblastomas

Abstract

EGFR amplification is a frequent genetic alteration in primary (de novo) glioblastomas, and is often associated with structural alterations. Most common is variant III (EGFRvIII), which results from a non-random 801 bp in-frame deletion of exons 2 to 7 of the EGFR gene. We assessed amplification and overexpression of EGFRvIII and wild-type EGFR in 30 glioblastoma biopsies. Immunohistochemically, EGFR overexpression was observed in 20 (67%) of 30 glioblastomas. Eight (27%) cases also showed immunoreactivity to an EGFRvIII antibody. In 6 of these cases, the pattern of EGFR and EGFRvIII overexpression was compared in serial sections: In 4 cases, areas with immunoreactivity to EGFRvIII largely coincided with wild-type EGFR expression. In the other 2 cases, the areas immunoreactive to EGFRvIII were significantly less extensive than EGFR-positive areas. To assess whether EGFRvIII is predominantly amplified in tumors with concurrent wild-type EGFR amplification, we carried our real-time quantitative PCR using 2 sets of primers located in exon 2 and intron 15 of the EGFR gene. A > 5-fold ratio of relative copy numbers between intron 15 (present both in wild-type EGFR and EGFRvIII) and exon 2 (present only in wild-type EGFR, but missing in EGFRvIII) suggested predominant amplification of EGFRvIII in only 3 (10%) of 30 glioblastomas. The observation that intratumoral wild-type EGFR overexpression is often more extensive and that predominant amplification of EGFRvIII is a rare event would limit the effectiveness of therapeutic approaches based on selective targeting of EGFRvIII.

Epidermal Growth Factor Receptor Variant III (EGFRvIII) Positivity in EGFR-Amplified Glioblastomas: Prognostic Role and Comparison between Primary and Recurrent Tumors

“…In line with previous studies, our IHC findings confirm that EGFR wild type protein expression is strong and widespread in EGFR-amplified glioblastomas (11,17,51). We did not assess regional heterogeneity of EGFR gene amplification.…”

In Situ Analysis of Mutant EGFRs Prevalent in Glioblastoma Multiforme Reveals Aberrant Dimerization, Activation, and Differential Response to Anti-EGFR Targeted Therapy

“…7, bottom middle). It would appear that regional EGFRvIII expression differences, as observed in other reports, are partly responsible for the presence of EGFRwt-EGFRvIII dimers in some areas and lack of heterodimer signal in other areas of the same tumor (30)(31)(32). We would therefore expect that some cells in the tumor samples tested were simply not coexpressing both EGFRwt and EGFRvIII and these cells failed to show EGFRwt-EGFRvIII heterodimer signal.…”

Identification of SOX2 as a novel glioma-associated antigen and potential target for T cell-based immunotherapy

“…Thus, ARF4L and GALT3 were markedly expressed in various normal tissues Tsuda et al, 2002) bearing the potential risk of autoimmune reactions. In addition, gp100, MAGE-1, TRP-2 and EGFRvIII were detectable only in a part of gliomas restricting the number of potentially treatable patients (Chi et al, 1997;Liu et al, 2003Liu et al, , 2004bBiernat et al, 2004). Owing to these limitations of several glioma-associated antigens and the heterogeneity of different types of malignant glioma (Chi et al, 1997;Nagane et al, 1997;Liang et al, 2005), the identification of additional target structures for CTLs is required.…”