Squamous Cell Carcinoma of the Skin Health Article

Definition

A squamous cell carcinoma is a skin cancer that originates from squamous keratinocytes in the epidermis, the top layer of the skin. Squamous is a term that indicates a surface with a scaly nature.

Description

Squamous keratinocytes are flattened, unpigmented skin cells in the middle of the epidermis. When they become cancerous, these cells invade the dermis (the layer of skin just below the epidermis) and spread out into the normal skin. They become visible as a small growth or area of change in the skin's appearance.

Most squamous cell carcinomas appear on areas that have been exposed to the sun: the head and neck, forearms, backs of the hands, upper part of the torso, and lower legs. Many develop in precancerous patches called actinic keratoses. Actinic keratoses are rough, scaly patches on the skin that usually start to show up in middle age. They are associated with a lifetime's exposure to the sun. Estimates of the chance that an actinic keratosis will turn into a squamous cell carcinoma vary from 0.24% to 20%.

Squamous cell carcinomas can also originate in old scars and burns, long-standing sores, and other areas of chronic skin irritation. These tumors tend to be more dangerous than those that arise in actinic keratoses.

The least dangerous type of squamous cell carcinoma is called Bowen's disease, intraepithelial squamous cell carcinoma, or squamous cell carcinoma in situ. Bowen's disease can show up anywhere on the skin, but it is especially common on the head and neck. This cancer usually grows slowly; but may evolve into a more serious, spreading form if it is not removed.

Other types of squamous cell carcinomas grow fairly quickly and can develop within a few months. These tumors may spread in the skin along the blood vessels, nerves, and muscles. They can also metastasize, or spread to other areas. On the average, 2-6% of squamous cell carcinomas metastasize, but this varies with the tumor site. At least 95% of the tumors that originate in actinic keratoses remain in the skin; but up to 38% of the cancers from scars are metastatic. Metastasis is also more likely when the cancer originates on the ear, lip, or genitalia, is large or deep, or develops in someone with a severely suppressed immune system. Cancers that regrow after treatment, and tumors that spread along the nerves are particularly dangerous.