Squamous cell carcinoma (SCC), the second most common skin cancer after basal cell carcinoma, afflicts more than 200,000 Americans each year. It arises from the epidermis and resembles the squamous cells that comprise most of the upper layers of skin. SCCs may occur on all areas of the body including the mucous membranes, but are most common in areas exposed to the sun.

Although SCCs usually remain confined to the epidermis for some time, they eventually penetrate the underlying tissues if not treated. When this happens, they can be disfiguring. In a small percentage of cases, they spread (metastasize) to distant tissues and organs and can become fatal. SCCs that metastasize most often arise on sites of chronic inflammatory skin conditions or on the mucous membranes or lips.

What Causes It

Chronic exposure to sunlight causes most cases of squamous cell carcinoma. That is why tumors appear most frequently on sun-exposed parts of the body: the face, neck, bald scalp, hands, shoulders, arms, and back. The rim of the ear and the lower lip are especially vulnerable to the development of these cancers.

Squamous cell carcinomas may also occur where skin has suffered certain kinds of injury: burns, scars, long-standing sores, sites previously exposed to X-rays or certain chemicals (such as arsenic and petroleum by-products). In addition, chronic skin inflammation or medical conditions that suppress the immune system over an extended period of time may encourage development of squamous cell carcinoma.

Occasionally, squamous cell carcinoma arises spontaneously on what appears to be normal, healthy, undamaged skin. Some researchers believe that a tendency to develop this cancer may be inherited.

Who Gets It

Anyone with a substantial history of sun exposure can develop squamous cell carcinoma. But people who have fair skin, light hair, and blue, green, or gray eyes are at highest risk. Those whose occupations require long hours outdoors or who spend extensive leisure time in the sun are in particular jeopardy. Dark-skinned individuals of African descent are far less likely than fair-skinned individuals to develop skin cancer.

More than two thirds of the skin cancers that individuals of African descent develop are SCCs, usually arising on the sites of preexisting inflammatory skin conditions or burn injuries. Although dark-skinned individuals of any background are less likely than fair-skinned individuals to develop skin cancer, it is still essential for them to practice sun protection.

Precancerous Conditions

Certain precursor conditions, some of which result from extensive sun damage, are worth noting. They are sometimes associated with the later development of SCC. They include:

Actinic, or solar, keratosis
Actinic keratoses are rough, scaly, slightly raised growths that range in color from brown to red and may be up to one inch in diameter. They appear most often in older people. Some experts believe that actinic keratosis is the earliest form of SCC.

Actinic cheilitis is a type of actinic keratosis occurring on the lips. It causes them to become dry, cracked, scaly, and pale or white. It mainly affects the lower lip, which typically receives more sun exposure than the upper lip.

Leukoplakia
These white patches or plaques on the tongue or inside of the mouth, arising in the mucous membranes, have the potential to develop into SCC. They are caused by sources of chronic irritation, including smoking or other tobacco use, and rough teeth or rough edges on dentures and fillings. Leukoplakia on the lips are mainly caused by sun damage.

Bowen’s disease
This is generally considered to be a superficial SCC that has not yet spread. It appears as a persistent red–brown, scaly patch which may resemble psoriasis or eczema. If untreated, it may invade deeper structures.

Regardless of appearance, any change in a preexisting skin growth, or the development of a new growth or open sore that fails to heal, should prompt an immediate visit to a physician. If it is a precursor condition, early treatment will prevent it from developing into SCC. Often, all that is needed is a simple surgical procedure or application of a topical chemotherapeutic agent.

Squamous cell carcinomas occur most frequently on areas of the body that have been exposed to the sun for prolonged periods. Usually, the skin in these areas reveals telltale signs of sun damage, such as wrinkling, changes in pigmentation, and loss of elasticity.

Warning Signs of Squamous Cell Carcinoma

A wart-like growth that crusts and occasionally bleeds.

A persistent, scaly red patch with irregular borders that sometimes crusts or bleeds.

An open sore that bleeds and crusts and persists for weeks.

An elevated growth with a central depression that occasionally bleeds. A growth of this type may rapidly increase in size.

A persistent, scaly red patch with irregular borders that sometimes crusts or bleeds.

An open sore that bleeds and crusts and persists for weeks.