Epidermal growth factor receptor gene and immunohistochemical expression in colorectal carcinomas

Expression of epidermal growth factor receptor (EGFR) protein can be found in normal colon mucosa, adenomas, and colon carcinomas. Its impact on prognosis in colorectal carcinomas is moderate, but the availability of a monoclonal antibody therapy designed to block EGFR has brought it into prominence in diagnostic histopathology. The literature reports a wide variance in expression of EGFR protein in primary tumours and metastases, ranging from <10% to almost 100%. Discordance in expression between the primary tumour and its metastases vary widely. EGFR gene mutations are rare. EGFR amplification and/or increased copy numbers have been reported and range from 4.5% to 30%. Most tumours seem to have a balanced EGFR copy number compared to chromosome 7 copy numbers (with a ratio of ∼1). Amplification of high copy numbers seems rare. The relationship between EGFR immunohistochemical expression and gene amplification and/or copy numbers is unresolved. Lack of standardization of investigation methods and procedures is probably a major cause of the divergent results.