Skin Cancer

Skin cancer is a disease in which rapidly multiplying, abnormal cells (cancer cells) are found in the outer layers of the skin.

What Is Skin Cancer?

In 1985, former president Ronald Reagan had a growth called a basal (BAY-zuhl) cell carcinoma removed from the side of his nose. The president had often been described as looking tanned and healthy, and when the news broke, it raised public awareness of skin cancer and the dangers of overexposure to the sun. Each year, about one million Americans are diagnosed with skin cancer.

The skin is the largest organ of the body. It protects people by keeping water and other fluids inside the body, by helping to regulate body temperature, by manufacturing vitamin D, and by performing a range of other complex functions. The skin also is a critically important barrier between people and such foreign invaders as bacteria. The skin is a basic part of physical appearance; it is the surface of the body that people present to the world.

Skin cancer is the most common of all cancers. It accounts for 50 percent of all cases of cancer. Cancers of the skin are divided into two general types: melanoma (mel-a-NO-ma) and nonmelanoma. Nonmelanoma are the most common cancers of the skin. They are also the most curable. Melanoma is much less common, but it is far more aggressive and causes 75 percent of all skin cancer deaths.

What Are the Types of Skin Cancer and Their Development?

Melanoma: 

The outer layer of the skin, the epidermis (ep-i-DER-mis), consists of layers of flat, scaly cells called squamous (SQUAY-muss)

cells, under which are round cells called basal cells. The deepest part of the epidermis consists of melanocytes (MEL-a-no-sites), which are the cells that give skin its color. Melanoma begins in the melanocytes.

Nonmelanoma:

The two main types of nonmelanoma are basal cell carcinoma and squamous cell carcinoma. These cancers develop in different layers of the skin, but they both appear more commonly on sun-exposed areas of the body. Squamous cell carcinomas grow more quickly than basal cell carcinomas.

How skin cancer develops: 

Skin cancer begins with damage to the DNA of the cells in skin. DNA is information people inherit from their parents that tells the cells of the body how to perform all the activities needed for life. DNA is contained in genes, and each cell has an identical set of genes. Some of these genes carefully control when cells grow, divide, and die. If a gene is damaged, the cell receives the wrong instructions or no instructions at all. When that happens, the cell can begin to grow and divide uncontrollably, forming an unruly cluster that crowds out its neighbors and forms a cancerous growth, or tumor. Melanoma is potentially serious because it has the ability to spread to other places in the body. Nonmelanoma, however, tends to stay put and is less likely to spread.

What Causes Skin Cancer?

Certain kinds of risk factors suggest who might be likely to develop cancer. A risk factor is anything that increases a person's chances of getting a disease.

Melanoma:

One risk factor is having certain types of moles. Another risk factor is having fair skin. The risk of melanoma is about 20 times higher for light-skinned people than it is for dark-skinned people. But dark-skinned people can still get melanoma. A person's chances of getting melanoma are greater if one or more close relatives have gotten it. People who have been treated with medicines that suppress the immune system (the body's defenses against infection) have an increased risk of developing melanoma. Exposure to ultraviolet* radiation-for example, sunlight, tanning lamps, and tanning booths-also is a risk factor for melanoma. Studies have shown no protective benefit of sunscreens in preventing melanoma.

Nonmelanoma:

Most cases of nonmelanoma are caused by unprotected exposure of the area that has the cancer to ultraviolet radiation. Most of this radiation comes from sunlight, but it may also come from artificial sources. Although children and young adults usually do not get skin cancer, they may get a lot of exposure to the sun that could result in cancer later on. Other risk factors for nonmelanoma include having fair skin and having a weakened immune system as a result of medical treatment for other conditions. In addition, exposure to certain kinds of chemicals increases a person's risk of getting nonmelanoma.