Xeroderma pigmentosum, and immunosuppressed individuals also have an increased incidence of neoplasm. The tumor generally appears in older individuals, and this is probably because aging causes a larger accumulation of sunlight over the years. Squamous cell carcinoma is also more prevalent in males than in females. In situ squamous cell carcinoma is generally restricted to the epidermis, and may extend into the dermis layer of the skin. Some lesions, which can develop into squamous cell carcinoma, are actinic keratosis and Bowen disease.
Actinic keratosis is a premalignant abrasion on the skin caused by prolonged exposure to sunlight.
Bowen's disease is a dysplasia of the basal layer of the dermis or carcinoma in situ often found on unexposed areas of the body and demonstrated by flat, reddish, scaly patches. These abrasions can grow to more than a centimeter in diameter, and usually do not attacking surrounding tissue and practically never metastasizing. Sweat glands and hair follicles can also play a role in skin cancer, but this is usually uncommon. Highly atypical cells at all levels of the epidermis typify squamous cell carcinoma in situ. When these squamous cell carcinoma cells break through this basement membrane, the course has become invasive.