Squamous cell carcinoma arises in the outer layer of the skin, the epidermis, causing mutations in cells called keratinocytes. UVB radiation is important for the induction of this skin cancer damaging DNA and its repair system, also causing mutations in tumor-suppressing genes. These mutated cells spread superficially and cause the appearance of the skin to change. When the mutated cells penetrate the dermis, the risk of metastasis increases.

Squamous cell carcinoma (SCC) is the second most common type of skin cancer. It occurs more often in men than in women at a 2:1 ratio. The incidence of squamous cell carcinoma among Caucasians in the UK is increasing. The incidence increases with age and the peak incidence of this skin cancer is at 66 years.

Click here to download the patient information sheet produced by the British Association of Dermatologists

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Caucasian patients who have lived in tropical countries for a prolonged are at higher risk of developing SCC.

Some common squamous cell carcinoma risk factors include:

* Chronic sun exposure mainly to UVB radiation but also UVA
* A premalignant condition called actinic keratosis or solar keratosis
* A suppressed immune system (transplants, lymphoma or leukaemia)
* Fair skin
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It usually occurs in areas exposed to the sun. Sunlight exposure and immunosuppression are the major risk factors for SCC of the skin with chronic sun exposure being the strongest environmental risk factor.

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The risk of metastasis (spread to lymph nodes or parts of the body) is low, but is much higher than basal cell carcinoma. Squamous cell cancers of the lip and ears have high metastatic and recurrence rate (20 to 50%). Squamous cell cancers of the skin in individuals on immunotherapy (especially transplant patients) or having lymphoproliferative disorders (leukaemias & lymphomas) are much more aggressive, regardless of their location.

Actinic or Solar Keratosis:
The earliest form of squamous cell carcinoma is called actinic (or solar) keratosis. Actinic keratoses appear as rough, red bumps on the scalp, face, ears, and backs of the hands. They often appear against a background of mottled, sun-damaged skin. They can be quite sore and tender, out of proportion to their appearance. In a patient with actinic keratoses, the rate at which one such keratosis may invade deeper in the skin to become a fully-developed squamous cell carcinoma is estimated to be in the range of 10%-20% over 10 years, though it may take less time. An actinic keratosis that becomes thicker and more tender raises the concern that it may have transformed into an invasive squamous cell carcinoma.
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