Protein overexpression and gene copy number of EGFR and HER2 in colorectal carcinoma

Abstract

To investigate the protein expression and gene copy number of EGFR and HER2, and the correlation between the two markers in colorectal carcinomas in Chinese. Total 42 samples of paraffin-embedded colorectal carcinomas in tissue microarray format were studied by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) for EGFR and HER2 protein expression and gene copy number status, respectively. Among 42 cases evaluated, EGFR scores were 0 in 18 cases, 1+ in 10 cases, 2+ in 5 cases and 3+ in 9 cases. HER2 expression was negative in 39 tumors, 1+ in 1 tumor, 2+ in 1 tumor and 3+ in 1 tumor. For FISH assessing EGFR, 18 (42.9%) cases showed no apparent copy number changes, including 14 (33.3%) cases of disomy and 4 (9.5%) cases of low trisomy, 24 (57.1%) cases showed increased gene copy numbers including high trisomy in 3/42 (7.1%), low polysomy in 9/42 (21.4%) and high polysomy in 12/42 (28.6%) cases. Gene amplification of EGFR is not detected. Four of 42 patients (9.5%) had increased HER2 gene copy number, including 3 patients with high polysomy and 1 patient with gene amplification. Significant association was not seen between EGFR protein expression and the gene copy number, nor between two markers and tumor differentiation. There was a highly significant concordance between the gene amplification and IHC 3+ for HER2 similar to that of breast cancer. Protein expression and/or increased gene copy number of EGFR is common in colorectal carcinomas but unrelated to pathological features in this cohort. HER2 protein overexpression and/or gene amplification are rare.