Protein overexpression and gene amplification of epidermal growth factor receptor in nonsmall cell lung carcinomas: Comparison of four commercially available antibodies by immunohistochemistry and fluorescence in situ hybridization study

Epidermal growth factor receptor (EGFR) overexpression in nonsmall cell lung carcinomas (NSCLC) is variable ranging from 19% to 89% and its prognostic value remains controversial. We tried to investigate (1) EGFR protein expression using four different antibodies, (2) the correlation between protein overexpression and EGFR gene amplification, and (3) the correlation between EGFR genetic status and clinicopathologic features in NSCLC. We examined EGFR protein expression using four different antibodies including Zymed EGFR kit (Clone 31G7), Dako EGFR pharmDx kit (Clone 2-18C9), Dako (Clone H11) and Novocastra (Clone EGFR 113) by immunohistochemical analysis. The protein overexpression was compared to gene amplification status by fluorescence in situ hybridization (FISH). EGFR protein overexpression was observed in 56% of tumors with Zymed EGFR kit, in 51% with Dako EGFR pharmDx kit, in 5% with Dako and in 18% with Novocastra (p = 0.010). Both Zymed and Dako pharmDx kit were more sensitive than the Dako test (clone H11) and Novocastra clone EGFR 113. EGFR overexpression was more prominent in squamous cell carcinomas (SCC) than adenocarcinomas (ADC) (71% vs. 48%, p = 0.001 with Zymed, 61% vs. 45%, p = 0.011 with Dako pharmDx kit; respectively). EGFR FISH-positivity as represented by high polysomy and gene amplification was observed in 45% of the NSCLC patients. Protein expression levels significantly correlated with the gene copy number per tumor cell (p < 0.001). Our data showed a higher percentage of positive cells detected by Zymed and Dako pharmDx tests. The EGFR protein overexpression rate varied from 4% to 72% according to different antibody clones and histologic types. EGFR protein expression detected by Zymed and Dako pharmDx was significantly associated with a high EGFR gene copy number.