Epidermal growth factor receptor - its expression and copy numbers of EGFR gene in patients with head and neck squamous cell carcinomas
Abstract
Signaling pathways activated by epidermal growth factor receptor (EGFR) are pathogenetically involved in the development of head and neck squamous cell carcinomas (HNSCC). A monoclonal antibody against the EGFR protein blocking the receptor activity (cetuximab - Erbitux - C225) is now available for therapeutic applications.
The mechanisms of EGFR protein overexpression are poorly understood. Regulatory pathways, EGFR gene structural changes or its amplification may be involved.
The aim of the study was to evaluate expression of the EGFR protein in patients with HNSCC, to identify EGFR gene copy numbers, and to find out whether the protein overexpression is associated with the EGFR gene amplification. In the case of a pathogenetical link of the EGFR gene amplification and the protein overexpression it would be useful to employ both diagnostic approaches to identify patients eligible for cetuximab therapy.
We investigated 33 patients with HNSCC. The expression of EGFR protein was evaluated by immunohistochemistry, copy numbers of EGFR gene and the numbers of chromosome 7 centromeric signals were investigated by fluorescence in situ hybridization on interphasic nuclei (I-FISH).
Histological sections from formalin fixed and paraffin embedded tissues were used. We observed three types of EGFR protein expression (homogeneous 3+ membrane positivity in 13 patients; membrane positivity varying from 1+ to 3+ in 12 patients; a strong membrane positivity at the periphery of the tumor cell clusters in 5 patients).
In two cases the results were difficult to interpret. In one case single tumor cells only were positive.
Numerical changes of chromosome 7 were present in 23 patients. We found the EGFR gene amplification in seven patients.
The tumor cells with amplification of the EGFR gene were generally infrequent and were localized in small clusters, or they were randomly dispersed between the tumor cell population without the gene amplification. We did not find any correlation between the EGFR gene amplification and the EGFR protein overexpression.
Thus, amplification of the EGFR gene is not pathogenetically involved in the EGFR protein overexpression. From the diagnostic aspect a standardized immunohistochemical assessment of the EGFR protein expression appears sufficient for detection of the EGFR status.
Criteria for cetuximab treatment in patients with HNSCC may differ from those already used for patients with colorectal carcinomas and should take different patterns of the EGFR protein overexpression into consideration.