Activation of EGFR signaling from pilocytic astrocytomas to glioblastomas

EGFR analyses allow for better correlation between genotype and phenotype in astrocytomas and represent an attractive therapeutic target. Most studies emphasize analyses of EGFR in glioblastomas (GBMs) but do not analyze all grades of astrocytomas (from pilocytic to GBM). The purpose of our study was to evaluate the status of EGFR (expression, deletion, and amplification) and EGFR protein expression in all grades of astrocytomas.

We analyzed a total of 145 surgical tumor specimens that included: 22 pilocytic astrocytomas, 22 grade II astrocytomas, 17 grade III astrocytomas and 84 GBMs. The specimens were compared to 17 non-neoplastic brain tissues obtained from epilepsy surgery. EGFR expression, EGFR amplification and EGFRvIII analyses were performed by quantitative real-time PCR, and protein expression was evaluated by immunohistochemistry.

EGFR relative overexpression and EGFR amplification were observed, respectively, in 50% and 20% of astrocytomas, while EGFRvIII was only found in GBMs (34.5%, p=0.005). Amongst EGFR-amplified GBM cases, 59% also presented EGFRvIII (p<0.001). Cytoplasmic accumulation of EGFR protein was detected in 75% of astrocytomas, and 21% of the astrocytomas showed nuclear localization (p=0.003).

EGFR alterations were found in all grades of astrocytomas, from pilocytic to GBMs, while EGFRvIII was exclusively found in GBMs. These findings provide important information on the mechanisms involved in the progression of astrocytomas for determining whether EGFR status can be used for effective and specific therapy.