Squamous Cell Carcinoma of th... 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.

Demographics

Squamous cell carcinomas are more common in the older adult population rather than the young. Overall, the chance of developing one is about 7% to 11%. The likelihood increases with exposure to the sun, and is greatest for fair-skinned individuals who tan poorly. Living near the equator, where ultraviolet light is more intense, also increases the risk. A weakened immune system— for instance, from an organ transplant, or AIDS—can also increase the risk of developing a squamous cell carcinoma by a factor of 5 to 250.

Squamous cell carcinomas tend to be most dangerous in individuals with dark skin. The mortality rate for African-Americans with squamous cell carcinomas is 17-24%, much higher than the 2% death rate for white males with nonmelanoma skin cancer. One reason for this disparity is that the cancers that develop in dark skin are more likely to come from old scars and burns than from actinic keratoses.

Causes and symptoms

Squamous cell carcinoma is caused by genetic damage to a skin cell. A number of factors can increase the risk that this will happen, but the exact cause is rarely known.

Any of the following changes may be a warning sign that an actinic keratosis is developing into a squamous cell carcinoma:

• pain
• increased redness
• sores or bleeding
• hardening or thickening
• increased size

Most squamous cell carcinomas begin as a small red bump on the skin. More advanced squamous cell carcinomas have the following characteristics:

• a few millimeters to a few centimeters in diameter
• reddish-brown, flesh-colored, pink, or red
• bumpy or flat
• sharp, irregular edges in Bowen's disease; others may have no definite edge
• may be crusted or scaly
• may contain bleeding sores

Diagnosis

Squamous cell carcinomas are usually diagnosed with a skin biopsy taken in the doctor's office. This is generally a brief, simple procedure. After numbing the skin with an injection of local anesthetic, the doctor snips out the tumor or a piece of it. This skin sample is sent to a pathologist to be read. It can take up to a week for the biopsy results to come back. Squamous cell carcinomas are graded into categories of one through four. The grading is based on how deeply the tumor penetrates in the skin and how abnormal its cells are. Higher grades are more serious.