What Is Non-Melanoma Skin Cancer?
Most cases of skin cancer are non-melanoma skin cancer. This category includes all types of skin cancer except malignant melanoma.
The skin is the body’s largest organ and helps fight infection and injury. It forms a porous barrier between the body’s internal structures and organs and the outside environment. The skin also helps regulate the body’s temperature.
Non-melanoma skin cancer usually starts when certain types of cells in the top layers of the skin (epidermis) become cancerous and begin to grow and divide without stopping. These cells create lumps (masses) called tumors. Cancerous tumor cells can spread to other parts of the body if they are not treated and eliminated.
Skin cancer is the most common type of cancer in the United States. More than 2 million cases of non-melanoma skin cancer are expected to be diagnosed in 2010, according to the American Cancer Society.
Anatomy of the Skin
The skin is the body’s largest organ and is its first line of defense against infection and injury. It forms a porous barrier between the body’s internal structures and organs and the outside environment. The skin helps to regulate the body’s temperature, provides protection from the elements, and wards off harmful microorganisms.
The skin is made up of two main layers, the epidermis and the dermis.
The epidermis is the outermost layer of skin. It consists mostly of flat cells called squamous cells, which make up the thickest part of the epidermis. Beneath these cells are round basal cells. In the deepest part of the epidermis are found melanocytes, which produce the pigment that gives skin its color.
Under the epidermis lies the dermis, where blood and lymph vessels are found. Also in this layer are sweat and oil glands. Sweat cools the skin surface, and an oily substance called sebum keeps the skin from drying out. Sweat and oil released by glands in the dermis reach the skin surface through tiny, tunnel-like holes called pores.
Types of Non-Melanoma Skin Cancer
Basal cell carcinoma makes up about 80 percent of all non-melanoma skin cancers. It starts in the basal cell layer, the deepest layer of the epidermis. It affects only those areas of the skin that produce hair. Most cases develop in areas of the skin that are often exposed to the sun. Basal cell carcinoma grows very slowly and rarely spreads to other parts of the body. Still, if left untreated, it can invade the deeper layers of the skin and can eventually spread into the underlying bone and other tissues.
Squamous cell carcinoma accounts for about 20 percent of non-melanoma skin cancers. It often develops from a premalignant (precancerous) lesion and may spread to other areas of the body. The most common areas affected by this cancer are the head, neck, and backs of the hands.
The earliest stage of squamous cell carcinoma is often referred to as Bowen’s disease. It shows up on sun-exposed skin as a sharply defined, reddish, scaly, flat area with an irregular border. First described in 1912 by Dr. John Bowen, Bowen’s disease can gradually develop over time into invasive squamous cell carcinoma. The risk factors and treatment for Bowen’s disease are the same as those for squamous cell carcinoma.
Other types of non-melanoma skin cancer are extremely rare and account for less than 1 percent of all cases of non-melanoma skin cancers:
- Sebaceous carcinoma is a type of cancer that forms in the sebaceous glands, the glands within the dermis that produce the skin’s natural oils. The disease can arise anywhere in the body where there are sebaceous glands, but about three-quarters of cases occur in the eye region, most often on an upper eyelid. Fewer than 500 cases of this cancer have been described, but it is aggressive. Left untreated, it has a high likelihood of spreading elsewhere in the body. Sebaceous carcinoma occurs most often in people age 40 to 60, but can also occur in younger persons. It may also occur more often in Asians than in other racial groups.
- Merkel cell carcinoma is extremely rare—fewer than 1,000 cases have occurred since the disease was first identified in the early 1970s. Nearly all cases (90 percent) affect persons over 50, and most cases are found in elderly persons. Because so few cases have occurred, risk factors for Merkel cell carcinoma are somewhat difficult to pinpoint. The risk of this cancer is thought to be increased if a person has had a previous case of basal or squamous cell carcinoma, a history of radiation treatment, or a suppressed immune system due to drugs or disease. Merkel cell carcinoma is an aggressive, rapidly spreading form of cancer. Even small growths can spread quickly, most often to nearby lymph nodes. From there the cancer can reach the brain, bone, lungs, and liver.
- Dermatofibrosarcoma protuberans occurs in only about 5 out of every 1 million people each year. Nearly all cases occur in adults 20 to 50 years old. Because of its rarity, risk factors are difficult to identify, but may include trauma (injury) to the skin, multiple immunizations in the same site, and burn and surgical scars. This is considered a moderately aggressive cancer that tends to spread only locally, and not to distant parts of the body. Its recurrence rate is high, however, even after successful initial treatment.
- Cutaneous angiosarcoma is another rare non-melanoma skin cancer, and one that is highly malignant. It is most common among the elderly and occurs two to three times more often in males than females. The risk of this cancer may be increased with radiation, herpes zoster infection (shingles), and exposure to certain chemicals.
Skin cancer is the most common and most rapidly increasing form of cancer in the United States, according to the American Cancer Society. It is estimated that 1 out of every 6 Americans will develop skin cancer at some point in their lives. New cases of non-melanoma skin cancer are increasing by 2 percent to 3 percent each year.
This content has been reviewed and approved by Myo Thant, MD.
This content was last reviewed
August 15, 2010 by Dr. Reshma L. Mahtani.