Squamous cell carcinoma (SCC) is a common type of skin cancer. It is derived from squamous cells, the flat cells that make up the outside layers of the skin, the epidermis. These cells are keratinising i.e., they produce keratin, the horny protein that makes up skin, hair and nails.
Invasive SCC refers to cancer cells that have grown into the deeper layers of the skin, the dermis. Invasive SCC can rarely metastasize (spread to distant tissues) and may prove fatal.
Invasive SCCs are usually slowly-growing, tender, scaly or crusted lumps. The lesions may develop sores or ulcers that fail to heal.
Most SCCs are found on sun-exposed sites, particularly the face, lips, ears, hands, forearms and lower legs.
They vary in size from a few millimetres to several centimetres in diameter. Sometimes they grow to the size of a pea or larger in a few weeks, though more commonly they grow slowly over months or years.
The majority of invasive cutaneous SCCs are due to exposure to ultraviolet radiation, which damages the DNA of fair-skinned individuals. SCCs most often arise within solar keratoses, and less often within Bowen's disease. Other risk factors for invasive SSC include:
- Inherited predisposition to skin cancer.
- Smoking - especially SCC of the lip.
- Thermal burn scars.
- Longstanding leg ulcers.
- Immunosuppression from drugs such as ciclosporin or azathioprine, especially in organ transplant recipients.
- Infection with human papillomavirus (HPV), the cause of viral warts, genital warts, and many mucosal SCCs. It is the cause of carcinoma cuniculatum but rarely causes other forms of cutaneous SCC.
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