Squamous Cell Carcinoma of the Skin

What Is It?

Squamous cells are small, flat skin cells normally found in the outermost layer of skin, called the epidermis. When squamous cells become cancerous (malignant), they typically develop into small, nodular or flat skin tumors, sometimes with a surrounding area of inflammation.

Most cases of squamous cell carcinoma are caused by unprotected, long-term exposure to the sun's ultraviolet rays. They usually occur on the sun-exposed skin of people who have spent a great deal of time outdoors, especially those with fair complexions and blue eyes. Occasionally, cancer develops within a scaly patch of sun-damaged skin called actinic keratosis, which has a pink, yellow or brownish tint.

Although most cases of squamous cell carcinoma are related to sun exposure, a smaller number develop in skin that has been injured or exposed to carcinogens (cancer-causing agents). Common locations for this type of squamous cell cancer include:

• Scars, burns, chronic (long-lasting) ulcers and other areas of skin injury
• The legs and torso, in workers exposed to arsenic or to industrial hydrocarbons, such as tar, soot, crude paraffin, anthracene or pitch
• Areas of the genitals affected by genital warts
• Areas of psoriasis treated with PUVA therapy, a combination of a light-sensitizing agent called psoralen and plus ultraviolet light
• The lips, mouth and larynx in smokers, where cancer growth is triggered by the carcinogens in tobacco

Most squamous cell carcinomas cause only a limited, localized area of skin damage, usually on a sun-exposed portion of the head or hand. In a small percent of cases, however, the cancer is more aggressive and spreads (metastasizes) to the lymph nodes and other parts of the body. Squamous cell carcinoma is most likely to spread when it is on the lips, ears, penis, scrotum or vulva.

Squamous cell carcinoma is the second most common skin cancer in the United States, with more than 200,000 cases each year. Since the early 1980s, the number of cases has risen dramatically, increasing at a rate of about 10 percent per year. People with weakened immune defenses are at especially high risk of developing squamous cell cancer. This includes people who are HIV positive, have received transplants or are taking immune-suppressing medications.

Symptoms

Squamous cell skin carcinoma usually appears as a tiny, painless nodule or patch that sometimes is surrounded by an area of inflammation. The surface of the cancer can be scaly, crusted or wartlike, and its center can form an open sore.

Although squamous cell carcinoma can develop on almost any part of the body, including the genitals and the soles of the feet, the most common locations are the head (scalp, lips, ears, inside the mouth) or the back of the hands or arms.