Squamous cell carcinoma is cancer that originates in the squamous cells of the skin.
Squamous cells (keratinocytes) are the main structural cells of the epidermis (the outer layer of skin). Squamous cell carcinoma, the second most common type of skin cancer, usually develops on sun-exposed areas but may grow anywhere on the skin or in the mouth, where sun exposure is minimal. It may develop on normal skin but is more likely to develop in precancerous skin growths caused by previous sun exposure (actinic keratoses—see Sidebar 1: Actinic Keratoses: Precancerous Growths). Each year in the United States, 700,000 people are diagnosed with squamous cell carcinoma and 2,500 people die from it.
Squamous cell carcinoma is characterized by its thick, scaly, irregular appearance. Fair-skinned people are much more susceptible to squamous cell carcinoma than darker-skinned people. This type of cancer is also more likely to develop in chronic sores—such as chronic skin ulcers—or in skin that has been scarred, particularly by burns.
Squamous cell carcinoma begins as a red area with a scaly, crusted surface that does not heal. As it grows, the tumor may become somewhat raised and firm, sometimes with a wartlike surface. Eventually, the cancer becomes an open sore and grows into the underlying tissue.
Bowen disease (intraepidermal squamous cell carcinoma):
Bowen disease is an early form of squamous cell carcinoma that is confined to the epidermis and has not yet invaded the deeper layers of the skin. Bowen disease most commonly occurs on sun-exposed areas of the skin but may occur anywhere. There may be many carcinomas or only a few. The affected skin is red-brown and scaly or crusted and flat, sometimes looking like a patch of psoriasis, dermatitis, or a fungal infection (called tinea or ringworm).
When doctors suspect squamous cell carcinoma or Bowen disease, they do a biopsy to differentiate this skin cancer from similar-looking diseases.
Prognosis and Prevention
Typically, the prognosis for small tumors that are removed early and adequately is excellent. Most squamous cell carcinomas affect only the area around them, penetrating into nearby tissues. However, some spread (metastasize) to distant parts of the body, nearby skin and lymph nodes, and eventually to nearby organs and can be fatal. Those that occur near the ears and lips, in scars, or around nerves are more likely to spread. However, about one third of cancers on the tongue or in the mouth have metastasized before diagnosis (see Mouth and Throat Cancer).
If the cancer is treated before it metastasizes, the person is usually cured. However, if the cancer has metastasized, the chance of surviving the next 5 years, even with treatment, is only 34%.
Because squamous cell carcinoma is often caused by sun exposure, doctors recommend that people stay out of the sun and use protective clothing and sunscreen, starting in early childhood.
Doctors treat squamous cell carcinoma and Bowen disease by scraping and burning the tumor with an electric needle (curettage and electrodesiccation), by cutting the tumor out, by destroying the cancer using extreme cold (cryosurgery), or by applying chemotherapy drugs to the skin. Doctors may also use photodynamic therapy (see see Sidebar 1: Using Lasers to Treat Skin Problems) or, occasionally, radiation therapy to treat squamous cell carcinoma. People whose squamous cell carcinomas have returned or are large should be treated with a technique called Mohs microscopically controlled surgery (see see Sidebar 1: Mohs Microscopically Controlled Surgery). These treatments are usually effective, and most people survive.
Squamous cell carcinoma that has spread to other parts of the body is treated with radiation therapy or chemotherapy, but treatment may not be effective.
Last full review/revision July 2013 by Gregory L. Wells, MD