Clinical significance of genetic alterations and expression of epidermal growth factor receptor (EGFR) in head and neck squamous cell carcinomas

Abstract

The significance of epidermal growth factor receptor (EGFR) signaling is well studied in a number of different tumors, but limited data is available with regard to head and neck squamous cell carcinoma (HNSCC). Since anti-EGFR therapies are currently under investigation in these malignancies as well, comprehensive information about the alteration of EGFR in HNSCC is necessary to design the most appropriate therapeutic protocols. We examined retrospectively the gene copy number of EGFR by FISH and the protein expression by immunohistochemistry using different epitope-specific antibodies in paraffin-embedded primary tumors of five different regions, from 71 HNSCC patients who had not been treated with anti-EGFR therapy. In seven cases corresponding lymph node metastases were also available for comparative analyses. We also determined the mutational status of tyrosine kinase (TK) domain (exon 19 and 21) and the extracellular deletion mutation (vIII) of EGFR, the KRAS mutation at codon 12 and the presence of HPV infection. Eight of the 71 cases (11.3%) showed EGFR gene amplification (most of them localized into the hypopharyngeal region) and the increased gene copy number (amplification+polysomy) was 43.7%. Despite pronounced intratumoral heterogeneity of EGFR protein expression being found, the high EGFR expression correlated with poor prognosis. On the other hand, the phosphorylation of EGFR was associated with prolonged survival. No mutations in the TK domain of EGFR were found in any of the HNSCC patients and only two cases were KRAS mutant at codon 12. We detected vIII deletion mutation of EGFR in 21% of the samples, but there was no statistically significant correlation between the presence of vIII mutant form and patient survival. EGFR vIII mutation was, however, associated with increased gene copy number. Fourteen of 71 cases (19.7%) were HPV-positive and the incidence of infection showed a decreasing tendency from the oral cavity towards the larynx. Interestingly, in contrast to previous findings, we could not observe improved survival in HPV-positive patients compared to non-infected patients, most probably due to the fact that the majority of these HNSCC patients were smokers and alcohol consumers. In conclusion, we found that increased EGFR protein levels and gene copy numbers (not gene amplification alone) have prognostic significance in the investigated HNSCC patient population. However, the relatively high incidence of the EGFR-vIII mutant form warrants careful therapeutic decision-making when choosing between different anti-EGFR treatment options.