EGFR expression and copy number changes in low T‐stage oral squamous cell carcinomas

Abstract

EGFR-directed therapies are used to treat patients with advanced head and neck squamous cell carcinoma (SCC). As it is still unclear whether or not EGFR amplification represents an early or late event in head and neck SCC progression, we aimed to determine the frequency of abnormalities of EGFR protein and gene copy numbers in early oral SCC. A tissue microarray of cancer tissue from 120 patients with pT1/2 oral SCC was constructed. We investigated EGFR protein expression by immunohistochemistry. EGFR gene copy enumeration was performed using fluorescence in-situ hybridization (FISH) and the novel automated silver in-situ hybridization (SISH) technology. Of early oral SCC, 19.3% showed high, 57.1% moderate and 23.6% low EGFR expression. EGFR amplification/polysomy was identified in 8% and 9% of cases by FISH and SISH, respectively. EGFR-SISH had a high concordance with EGFR-FISH (kappa value = 1.0), and both methods showed high conformity with EGFR immunohistochemistry (P = 0.001 and P = 0.006, respectively). No correlation was found of EGFR protein expression or gene amplification status with pT or pN stage. Only a small subgroup of early oral SCC is characterized by EGFR amplification, which can be identified reliably using EGFR-SISH technology. This finding suggests that EGFR gene amplification mostly occurs in advanced stages of oral SCC.