SQUAMOUS CELL CARCINOMA (SCC)
This Tumours is derived from epidermal keratinocytes. The incidence of squamous cell carcinoma shows marked geographical variation. It is most frequent in parts of the world where light-skinned people are exposed to large cumulative exposures to sunlight. Thus, it is much more frequent in southern than northern states of America, in outdoor workers, and the incidence is much higher in light-skinned than in dark-skinned peoples (Carrucci 2004).
Genetic variation accounting for pigmentation of the skin and reaction to sun exposure as described above is therefore also thought to be important in determining susceptibility. Albino individuals are particularly at risk, especially if they live in the tropics. Arsenic, tar, and oil derivatives and X- rays and gamma rays also predispose to squamous cell carcinoma. In the UK, SCCs occurring as a result of exposure to these carcinogens have become significantly less common as working conditions in relevant industries have improved. Squamous cell carcinomas are more common in chronically immunosuppressed individuals, and organ transplant recipients now represent a significant proportion of patients with multiple SCC. There is some evidence that the risk is particularly high in those treated with azathioprine as a result of higher incorporation of a metabolic product of azathioprine into skin cell DNA (Kalra et al. 2011), and the move to replacing this drug with others may reduce the incidence in the future.
SCC may also arise in chronic scars, ulcers, and sinuses, but as these chronic conditions are better controlled, this is now much less frequent in the developed world. SCC is still seen however in medical conditions where scarring cannot be controlled such as hereditary skin disorders that cause blistering and ulceration (e.g., epidermolysis bullosa) and conditions associated with leukoplakia, such as dyskeratosis congenita and lichen sclerosus et atrophicus.
Squamous cell carcinoma may also occur in the ectodermal dysplasias, the Rothmund–Thomson syndrome, sclerotylosis, and hyperkeratosis lenticularis perstans. Genetic disorders predisposing to cutaneous squamous cell carcinoma may also predispose to squamous cell carcinoma in the mucous membranes, e.g., dyskeratosis congenita and ectodermal dysplasia can predispose to tongue, esophageal, and cervical carcinoma.