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Dysregulation of epidermal growth factor receptor in actinic keratosis and squamous cell carcinoma.

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase. Its correct function is required for normal skin development and homeostasis, while dysregulation of EGFR signalling results in cellular hyper-proliferation and defects in differentiation, leading to impaired wound healing, the development of psoriasis-like lesions, structural and functional defects of hair follicles and tumourigenesis. Actinic keratosis, which is also known as solar keratosis, develops in sun-exposed areas of the skin. These are often called 'premalignant lesions' and are said to represent early squamous cell carcinoma (SCC) in situ, although debate over their classification continues. Anti-EGFR therapies have been approved for the treatment of several malignancies and are undergoing trials for others [1], including advanced cutaneous squamous cell carcinoma (CSCC). However, a number of questions remain regarding the treatment of CSCC with anti-EGFR inhibitors. A lower number of CSCC tumours are EGFR positive in comparison to other types of tumours, such as head and neck SCC (HNSCC), and it has been suggested that patients should be selected on the basis of high tumour EGFR expression. However, there are reports of patients with tumours showing no EGFR-positive staining responding to anti-EGFR therapy. EGFR is an oncogenic driver in many tumours. Does it drive the transformation of actinic keratosis to a tumourigenic phenotype? Many such questions remain, and here, we discuss the role of EGFR in SCC and its functions during the different stages of skin cancer development.