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EGF Receptor (EGFR): Function and Clinical Role

The EGF receptor (EGFR) is a cell surface protein that transmits growth signals. Mutations in this receptor play a key role in several types of cancer.

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Things worth knowing about "EGF Receptor"

The EGF receptor (EGFR) is a cell surface protein that transmits growth signals. Mutations in this receptor play a key role in several types of cancer.

What is the EGF Receptor?

The EGF receptor (abbreviated EGFR, standing for Epidermal Growth Factor Receptor) is a protein located on the surface of many cell types throughout the body. It belongs to the receptor tyrosine kinase family and plays a central role in regulating cell growth, division, and survival. Its natural binding partner is the epidermal growth factor (EGF), a signaling molecule that stimulates cell proliferation.

In medicine, EGFR is particularly important in the context of cancer development and treatment. Excessive activity or mutations of this receptor can lead to uncontrolled cell growth and tumor formation.

Structure and Mechanism of Action

The EGF receptor is a transmembrane glycoprotein consisting of three main regions:

Extracellular domain: Binds EGF and other growth factor ligands such as TGF-alpha.
Transmembrane domain: Anchors the receptor within the cell membrane.
Intracellular tyrosine kinase domain: Transmits the signal into the cell interior upon activation.

When EGF binds to the receptor, two receptor molecules come together (dimerization), activating the intracellular tyrosine kinase. This triggers a signaling cascade that activates pathways such as RAS/MAPK and PI3K/AKT, which control cell growth, survival, and differentiation.

Clinical Significance and Cancer

EGFR mutations or overexpression have been identified in several cancer types:

Non-small cell lung cancer (NSCLC): EGFR mutations are especially frequent and therapeutically relevant here.
Colorectal cancer: EGFR overexpression is common, but RAS mutation status is critical for therapy selection.
Head and neck squamous cell carcinoma (HNSCC): High EGFR expression is associated with poorer prognosis.
Breast cancer and glioblastoma: EGFR alterations also play a role in these tumor types.

Overexpression means that more receptors than normal are present on the cell surface, leading to amplified growth signals. Activating mutations cause the receptor to remain permanently active even without ligand binding.

Diagnosis and EGFR Testing

Determining EGFR status is an important part of diagnostics in certain cancers, as it directly influences treatment decisions. The following methods are used:

Molecular pathology: Analysis of tumor tissue (biopsy) for EGFR mutations using PCR or sequencing.
Liquid biopsy: Detection of EGFR mutations in blood (circulating tumor DNA).
Immunohistochemistry (IHC): Detection of EGFR protein expression in tissue samples.

The results of these tests are decisive for whether a patient may benefit from targeted therapy.

Treatment: EGFR Inhibitors

Given the central role of EGFR in tumor development, specific inhibitors have been developed that selectively interfere with this signaling pathway. Two main classes are distinguished:

Tyrosine Kinase Inhibitors (TKI)

These small molecules block the intracellular kinase activity of the receptor. Well-known agents include erlotinib and gefitinib (1st generation), afatinib (2nd generation), and osimertinib (3rd generation, effective also against the T790M resistance mutation). They are primarily used in non-small cell lung cancer.

Monoclonal Antibodies

These antibodies bind to the extracellular domain of EGFR and block ligand binding. Important representatives include cetuximab and panitumumab, which are used in colorectal cancer and head and neck tumors.

Resistance Development

A common challenge in EGFR-targeted therapy is the emergence of resistance mutations, such as the T790M mutation in lung cancer, which can render first- and second-generation TKIs ineffective. Newer agents like osimertinib were specifically designed to overcome this resistance mechanism.

Side Effects of EGFR Inhibitors

Because EGFR is also expressed in healthy tissues, particularly in the skin and gastrointestinal tract, EGFR inhibitors can cause characteristic side effects:

Acneiform rash: A skin rash that is often considered a sign of treatment efficacy.
Paronychia: Inflammation of the nail folds.
Diarrhea: Especially common with oral TKIs.
Stomatitis: Inflammation of the oral mucosa.
Rarely: Interstitial lung disease (ILD).

References

Herbst RS, Morgensztern D, Boshoff C. The biology and management of non-small cell lung cancer. Nature. 2018;553(7689):446-454.
Hynes NE, Lane HA. ERBB receptors and cancer: the complexity of targeted inhibitors. Nature Reviews Cancer. 2005;5(5):341-354.
World Health Organization (WHO). Cancer - Targeted Therapy Overview. WHO Technical Report. Geneva, 2022.

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