Skin Cancer Types and Their Features

Basal cell carcinoma, squamous cell carcinoma, and melanoma make up the vast majority of all skin cancers.

These three cancers have several things in common:

• They are predominantly linked to excessive exposure to ultraviolet (UV) rays, either from sunlight or tanning beds.
• They are all associated with many of the same additional risk factors, including fair skin that freckles or burns easily.
• When treated at the earliest stage, they are all almost always curable.

But each type of cancer originates in a different kind of skin cell and develops in a unique way. Each also varies in how likely it is to spread to other parts of the body — a dangerous progression.

Basal Cell Carcinoma: The Most Common

Basal cell cancer accounts for an estimated 80 percent of all cases of skin cancer, (1) with an estimated 3.6 million cases diagnosed in the United States each year.

This cancer develops in basal cells, which are located in the outermost layer of skin (the epidermis). Basal cells continually divide, move up in the epidermis, and flatten, morphing into a different kind of skin cell called a squamous cell.

Basal cell carcinoma generally appears in areas of the body that are habitually exposed to the sun, particularly the face, ears, neck, scalp, shoulders, and back. The backs of the hands can also be a trouble zone.

Rarely, basal cell cancer will develop on a part of the body that isn’t exposed to the sun; researchers don’t know why.

Basal cell cancer grows very slowly. Left untreated, however, a growth can widen and deepen significantly, becoming unsightly or causing functional problems.

It is unlikely that a basal cell carcinoma will become life-threatening. But it can happen: It is estimated that about 2,000 people in the United States die each year from basal cell and squamous cell cancers combined, although this number has been dropping in recent years. (2)

People who develop basal cell cancer are more likely to have recurrences over time. (1)

Squamous Cell Carcinoma: More Likely to Go Deeper

Squamous cell cancers account for around 20 percent of all cases of skin cancer, (1) with an estimated 1.8 million cases in the United States each year. (2)

The cancer affects squamous cells, which are located at the top of the epidermis. The body continually sloughs off old squamous cells and replaces them with new ones.

Like basal cell carcinoma, the squamous cell kind usually develops in areas that get sun exposure on a regular basis: face, ears, neck, lips, scalp, and the backs of the hands.

The skin in these areas will often show other signs of sun damage, including wrinkles, age spots, and broken blood vessels.

Squamous cell cancer can grow on the sites of preexisting inflammatory skin conditions or burn scars, particularly in African-Americans. (4)

These carcinomas can also develop in mucous membranes or the genital area. Most of the squamous cell cancers that are in the genital region may be related to infection with certain types of human papilloma (HPV) virus. (5)

Compared with basal cell carcinoma, squamous cell cancer is more likely to grow into deeper layers of skin and to spread.

While the risk of metastasis is very low, it is real, especially for the elderly and people with compromised immune systems. (2)

Many doctors consider dome-shaped tumors called keratoacanthomas to be a form of squamous cell cancer. These growths sometimes develop on skin that has been exposed to the sun.

While keratoacanthomas enlarge quickly, their growth typically slows. Some tumors go away on their own; others continue to get bigger; and a few may spread to other parts of the body. (1)

Squamous Cell Precancers: Be on the Lookout

The following conditions are potential signs of squamous cell carcinoma; some may even be considered very early forms of this cancer.

The major risk factor for all of them is excessive UV exposure.

• Actinic, or Solar, Keratoses These rough, scaly, slightly raised growths typically develop in older people who’ve spent decades in the sun. According to some estimates, 40 to 60 percent of squamous cell cancers begin as untreated actinic keratoses.
• Actinic Cheilitis This is a form of actinic keratosis that develops on the lower lip, resulting in dry, cracked, scaly, and pale or white skin.
• Leukoplakia This condition affects the mucous membranes inside the mouth, causing white patches on the tongue, gums, or cheeks.
• Bowen’s Disease This condition may appear as a red-brown, scaly patch resembling psoriasis or eczema. The cause may be sun exposure or exposure to arsenic, but other triggers include radiation, chemical carcinogens, genetics, trauma, or exposure to certain HPV viruses. (4)

Melanoma: Rare but Potentially Deadly

Melanoma is rare compared with basal cell and squamous cell carcinomas, accounting for only about 1 percent of all cases, or an estimated 100,000 cases annually in the United States. (6)

This cancer develops in the pigment-producing cells in the epidermis called melanocytes that are also responsible for moles, many of which are harmless.

But having a large number of moles is a melanoma risk factor.

Melanoma is more dangerous than other skin cancers because it is much more likely to spread.

Immunotherapy, targeted treatments that focus on the genetics of tumors, and other medical breakthroughs are prolonging the lives of people with advanced melanoma, not just by months but by years. But metastatic melanoma can still be a tough disease to beat, with more than 7,000 U.S. deaths annually. (6)