Protein overexpression and gene amplification of HER-2 and EGFR in colorectal cancers: an immunohistochemical and fluorescent in situ hybridization study

Abstract

Overexpression of HER-2 and the epidermal growth factor receptor (EGFR) has been observed in many cancers, sometimes accompanied by gene amplification. To assess whether novel chemotherapies targeting these overexpressed proteins may be effective for the treatment of colorectal cancers, we examined the exact frequency of HER-2 and EGFR overexpression, the relationship between gene amplification and protein expression, and the heterogeneity of gene amplification within and between primary and metastatic tumors. We evaluated 244 colorectal cancers immunohistochemically. All tumors found to overexpress HER-2 or EGFR were further analyzed for gene amplification by fluorescent in situ DNA hybridization. Overexpression of HER-2 and EGFR was found in 8 (3%) and 19 (8%) of the 244 colorectal carcinomas, respectively. Gene amplification was observed in 100 and 58% of the tumors exhibiting HER-2 and EGFR overexpression, respectively. HER-2 amplification in cancer cells was characterized by clusters of hybridization signals, suggesting amplicons in homogeneously staining regions that were predominant in most primary and metastatic tumors. EGFR amplification, observed as scattered signals reminiscent of amplicons in double minute chromosomes, or coamplification of EGFR with the centromeric regions was observed as a minor population within primary tumors, and found in variety of populations in metastatic tumors. Overexpression of HER-2 and EGFR were observed in only a small fraction of colorectal carcinomas, but were frequently accompanied by gene amplification. The HER-2 gene is located on chromosomal region 17q11.2-q12 and the EGFR gene is located on 7p12. These encode 185 kDa (p185) and 170 kDa plasma membrane glycoproteins, respectively. They share approximately 50% overall homology and are composed of an N-terminus extracellular ligand-binding domain, a transmembrane lipophilic segment, and a C-terminus intracellular region containing a tyrosine kinase domain.

Epidermal growth factor receptor expression and gene amplification in colorectal carcinoma: an immunohistochemical and chromogenic in situ hybridization study

“…The frequency of gene amplification, on the other hand, is only 12% in primary colorectal carcinomas and 8% in metastases. The presence of a small but defined proportion of colorectal cancers that show EGFR gene amplification is in agreement with a recent report that used fluorescent in situ hybridization and IHC, 32 but differ from earlier studies that used Southern blot-or polymerase chain reaction (PCR)-based methods. In studies that used Southern blotting 33 or PCR, 34 no gene amplification was demonstrated in colorectal carcinoma cell lines or tissues microdissected from paraffin blocks, despite the presence of protein expression.…”

Close association between HER-2 amplification and overexpression in human tumors of non-breast origin

“…For example, HER-2 overexpression was shown in 5.7-88.8% of non-small-cell lung cancers 10,11 and 3.0-54% of colon cancers. 12,13 To a smaller extent, this variability is also observed in amplification analysis. Different methods for analysis (Southern blot or fluorescent in situ hybridization (FISH)) and definitions of amplification have resulted in variable frequencies of amplification reported in the literature such as 0-66% in ovarian cancer 14,15 or 6-56.2% in breast cancer.…”

Salivary gland-type lung carcinomas: an EGFR immunohistochemical, molecular genetic, and mutational analysis study

“…Some studies have suggested that the mechanisms of EGFR protein overexpression vary depending on tumor type. For example, gene amplification has been implicated as a major cause of EGFR protein expression in glioblastomas, 22 esophageal squamous cell carcinoma, 23 and colon carcinoma, 24 whereas the relationship between EGFR protein expression and gene amplification or mutation is not clearly understood in lung carcinoma. Some studies observed that somatic mutations of EGFR tyrosinekinase domain of non-small-cell lung carcinomas were associated with immunoexpression, 6 while other studies have shown that overexpression of EGFR was better associated with EGFR amplification or polysomy.…”