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The Epidermal Growth Factor Receptor (EGFR) Pathway - Gene and Protein Alterations

The Epidermal Growth Factor Receptor (EGFR; also known as EGFR1 and HER1) is a validated anticancer target, against which there are several new agents currently licensed for use, and many newer agents in various stages of development. The importance of EGFR lays in its key role as a receptor tyrosine kinase, controlling two major cellular signalling pathways, one stimulating cell proliferation and growth, and the other controlling the so-called survival pathway (see figure below).

In a variety of cancers these pathways appear to be dysfunctional. This can arise in a number of ways; through chronic activation of the EGFR receptor itself, or through the presence of activating mutations in certain genes encoding downstream intermediates in the two pathways activated by EGFR, namely RAS, RAF, and PI3K.

A breast tumour immunostained for EGFR with the DAKO PharmDx kit

EGFR - Immunohistochemical Detection of Receptor Protein

In colorectal cancer there is evidence that response to the EGFR-targeting antibody treatments cetuximab (Erbitux™) and panitumumab (Vectibix™) is linked to over-expression of EGFR, and the labelling of these agents suggests that they are suitable only for patients who demonstrate over-expression of EGFR protein as detected by immunohistochemistry.

While the picture is less clear in breast cancer, some relationships have been established. Activating mutations of the EGFR gene are not seen in breast cancer, nor is amplification common. However; a significant proportion of breast cancers do show enhanced expression of EGFR protein by immunohistochemistry; these tumours are often high grade, hormone receptor-negative, and with high proliferation. It has been suggested that these patients might benefit from anti-EGFR-targeted therapies.

Source BioScience has extensive experience in EGFR evaluation, and offers immunohistochemical testing of EGFR protein expression in FFPE tumour samples using the CE-marked DAKO PharmDx kit. Tumour samples immunostained for EGFR are assessed visually by a registered pathologist and assigned a semi-quantitative score based upon criteria of staining intensity and distribution, using an FDA-approved algorithm.

References:

• Jimeno and Hidalgo (2006) Pharmacogenomics of epidermal growth factor (EGFR) inhibitors. Biochim Biophys Acta 1766:217
• Cappuzzo et al. (2005) Epidermal Growth Factor Receptor gene and protein and gefitinib sensitivity in non-small-cell lung cancer. J Natl Cancer Inst 97:643
• Chan et al. (2006) The role of the epidermal growth factor receptor in breast cancer. J Mammary Gland Biol Neoplasia 11:3

EGFR - FISH Testing for Gene Copy Number

A breast tumour processed for EGFR FISH. Copies of the EGFR gene are seen as red dots against the deep blue of individual cell nuclei. The red spots represent markers for chromosome 7. In a normal cell there is usually 2 copies of each.

In non-small-cell lung cancer there is compelling evidence that response to both gefitinib (Iressa™) and erlotinib (Tarceva™) is associated with EGFR gene copy number, as well as with the presence of certain activating mutations of the EGFR gene. The picture is less clear with respect to the expression of the receptor protein itself, and the use of immunohistochemistry to evaluate levels of expression is of questionable utility.

In colorectal cancer there is also evidence that response to the EGFR-targeting antibody treatments cetuximab (Erbitux™) and panitumumab (Vectibix™) is linked to gene copy number, as detected by Fluorescence In Situ Hybridisation (FISH). In addition, for these agents it is suggested that they are suitable only for patients who demonstrate over-expression of EGFR protein, as detected by immunohistochemistry.

Source BioScience offers a validated, standardised EGFR FISH test, which can be used to demonstrate EGFR gene amplification or increased copy number due to polysomy. FISH evaluation to identify EGFR gene amplification is assessed visually over a number of representative areas within the sample to account for heterogeneity. The sample is assigned a score in the form of a ratio, relating the number of copies of the EGFR gene to the number of copies of chromosome 7. A score of > 2 indicates gene amplification.

References:

• Cappuzzo et al. (2005) Epidermal Growth Factor Receptor gene and protein and gefitinib sensitivity in non-small-cell lung cancer. J Natl Cancer Inst 97:643
• Moroni et al. (2005) Gene copy number for epidermal growth factor receptor (EGFR) and clinical response to antiEGFR treatment in colorectal cancer: a cohort study. Lancet Oncol 6:279

EGFR - Gene Mutation Analysis

Image of real-time PCR readout for EGFR gene mutations using the DxS Therascreen EGFR29 kit

Source BioScience offers EGFR mutation testing based on the CE-IVD marked Therascreen™ EGFR29 Mutation Test. This test is suitable for FFPE archival material, and detects the 29 most common somatic mutations found in the EGFR gene. In particular deletions in exon 19 and, in exon 20, the L858R pointy mutation, make tumours more sensitive to the small molecule inhibitors of EGFR gefitinib and erlotinib. The results of mutation tests are reported as positive or negative for the presence of a particular mutation and the relative frequency of that mutation in the tumour sample.

Note: There is a growing body of evidence that certain inherited gene alterations (SNPs or single nucleotide polymorphisms) in the EGFR gene may be linked to treatment response in breast and lung cancers. Testing for polymorphisms is also available through Source BioScience. For further details, please contact us: pharma

References:

• Jimeno and Hidalgo (2006) Pharmacogenomics of epidermal growth factor (EGFR) inhibitors. Biochim Biophys Acta 1766:217
• Cappuzzo et al. (2005) Epidermal Growth Factor Receptor gene and protein and gefitinib sensitivity in non-small-cell lung cancer. J Natl Cancer Inst 97:643.

For further information please contact us at: Pharma