Changes in the EGFR amplification and EGFRvIII expression between paired primary and recurrent glioblastomas

Abstract

Background: The efficacy of novel targeted therapies is often tested at the time of tumor recurrence. However, for glioblastoma (GBM) patients, surgical resections at recurrence are performed only in a minority of patients; therefore, molecular data are predominantly derived from the initial tumor. Molecular data of the initial tumor for patient selection into personalized medicine trials can therefore be used only when the specific genetic change is retained in the recurrent tumor.

Methods: In this study we determined whether EGFR amplification and expression of the most common mutation in GBMs (EGFRvIII) is retained at tumor recurrence. Because retention of genetic changes may be dependent on the initial treatment, we only used a cohort of GBM samples that were uniformly treated according to the current standard of care (ie, chemo-irradiation with temozolomide).

Results: Our data show that, in spite of some quantitative differences, the EGFR amplification status remains stable in the majority (84%) of tumors evaluated. EGFRvIII expression remained similar in 79% of GBMs. However, within the tumors expressing EGFRvIII at initial diagnosis, approximately one-half lose their EGFRvIII expression at tumor recurrence.

Conclusions: The relative stability of EGFR amplification indicates that molecular data obtained in the primary tumor can be used to predict the EGFR status of the recurrent tumor, but care should be taken in extrapolating EGFRvIII expression from the primary tumor, particularly when expressed at first diagnosis.

Keywords: EGFR; EGFRvIII; glioblastoma; recurrent tumors.

Fig. 1.

(A) Variability of EGFR amplification within biological replicates. As can be seen, the EGFR status between replicates was relatively constant in our samples. (B) EGFR amplification of primary versus recurrent glioblastomas. Although EGFR amplification varied between the primary and recurrent tumor, the difference was generally within 2.5 ΔCt values (dotted lines) of each other. (C) EGFRvIII expression, plotted as a percentage of all EGFR transcripts, is predominantly observed in samples with EGFR amplification (ie, those with dCt >3). Points in dark grey are from initial diagnoses, and light grey is from the recurrent tumor. (D) EGFRvIII expression in primary versus recurrent tumors. As can be seen, the relative expression of EGFRvIII was often lower in recurrent tumors than in primary tumors, with 7 samples showing EGFRvIII expression only in the primary tumor.

Fig. 2.

Correlation between EGFR amplification status (x-axis) and EGFR gene expression levels (y-axis) as determined by quantitative reverse-transcriptase PCR on tumor DNA or RNA.