The skin consists of three layers. The top layer, called the epidermis, is where most skin cancers, including squamous cell carcinoma, arise. Below that is the dermis, the layer that contains sweat glands, oil glands, and other structures of the skin. The subcutaneous layer, which is below the dermis, is composed of fat and connective tissue and connects the skin to the underlying muscle.
Squamous cell carcinomas are most commonly found on areas of the body that are frequently exposed to the sun, including the ears, face, and mouth. They tend to occur in people who are older than do basal cell tumors. This type of skin cancer often arises from a type of precancerous lesion known as an actinic keratosis (sometimes called solar keratosis), which appears as a rough, flat pink spot. Actinic keratoses are caused by overexposure to the sun. Most actinic keratoses cause no symptoms, do not become cancerous, and eventually slough away. If the lesion does become cancerous, it is usually raised above the normal skin surface and is firmer to the touch. Squamous cell tumors can be more aggressive than basal cell tumors and are slightly more likely to spread to other parts of the body.
