Types of Skin Cancer

Epidemiology and Etiology of Skin Cancer

Cancer of the skin is generally divided into two broad categories: melanoma and nonmelanoma cancers. Nonmelanoma cancers account for about 80 percent of skin malignancies. The most common nonmelanoma cancers are Basal Cell Carcinoma (BCC) and Squamous Cell Carcinoma (SCC), but other tumors of sweat glands, hair follicles, or virtually any other structure of the skin may also be included.

Some estimates suggest that up to half of all Americans who reach the age of 65 will have some type of skin cancer at least once. The lifetime probability of developing a skin malignancy varies by sex, geographic area of residence, and cancer type. Risk factors for cancer of the skin include:

• exposure to ultraviolet radiation (this includes tanning beds and tanning lamps, as well as sunlight)
• residence in so-called "sunbelt" areas, i.e., latitudes closer to the equator
• dysplastic nevi
• family history/genetic anomalies
• history of severe sunburn
• fair skin
• history of x-ray or radiation burns
• occupational exposure to coal tar, pitch, creosote, arsenic compounds, or radium
• immunocompromised status

Exposure to ultraviolet radiation from the sun is a major risk factor for all the principal types of skin cancer. Persons at greatest risk are those with fair skin, light hair, light eyes, and the genetic phenotype most susceptible to sunburn. Living closer to the equator increases the risk, as does participation in outdoor activities. However, the specific risk varies with the type of cancer.

Epidemiologic data suggest that the risk of developing Malignant Melanoma (MM) is specifically related to the amount and intensity of sun exposure during adolescence. A person who experienced three or more severe, blistering sunburns during those years has a risk of developing MM four to five times greater than that of the general population.

Individuals whose sun exposure is sporadic summertime trips to the beach for example, have a greater risk for MM, but people whose exposure to sun is constant, such as farmers or road-construction workers, are more at risk for BCC or SCC. Malignant tumors of all types may also develop years after x-ray or radium burns or occupational exposure to coal tar, pitch, creosote, arsenic compounds, or radium.

Xeroderma pigmentosum is a rare, chronic, progressive, pigmentary and atrophic disease. It is inherited as an autosomal recessive trait involving a defect in the enzymes active in the excision and repair of DNA damaged by ultraviolet radiation. In this disease, the eyes and skin are extremely sensitive to light. Xeroderma pigmentosum begins in childhood, and early development includes a number of serious problems, among which might be melanoma, BCC, or SCC. Patients with this disease have about a three-fold increased risk of developing some type of skin cancer.

African Americans and others with dark skin rarely develop skin cancer, but when it does occur, it most commonly develops under the fingernails or toenails or on the soles or palms. Risk factors include exposure to sunlight, albinism, burn scars, preexisting pigmented lesions, and chronic discoid lupus erythematosus.

Although most skin cancers can be removed surgically, your specific treatment will depend on the type of cancer you have, its stage of growth, and its location on your body. Skin cancer is diagnosed by removing all or part of the growth and examining its cells under a microscope. Plastic surgeons treat all of the following types of skin cancers:

Basal Cell Carcinoma

Basal cell carcinoma accounts for more than 90 percent of all skin cancers in the United States. The lifetime probability of developing BCC is 11 to 28 percent. The risk is similar for males and females when they are young, but after the age of 45, men are more likely to develop BCC than women (male/female age adjusted incidence ratio =1.6).

Areas that are exposed - the head, face and neck, arms and hands - are the most common sites for BCC, with the tumor often arising on the nose. Basal cell carcinomas are slow-growing and rarely metastasize, but they can invade or impinge upon underlying orifices (e.g., eyes, ears, mouth) or structures (e.g., bone, dura mater).

Squamous Cell Carcinoma

There are about four cases of BCC for every one of SCC; the lifetime probability of developing SCC is 1.5 to 11 percent. Males are at greater risk for SCC throughout their lifetimes than are females (male/female age-adjusted incidence ratio = 2.8). As people age, their risk for developing SCC rises, so overall, older people of either sex are at greater risk.

Like BCC, SCC predominates on exposed areas like the head, face, and neck, but may occur anywhere on the body. Squamous cell carcinoma arises from the malpighian cells of the epithelium.

Although there are fewer cases of SCC than BCC, the potential for metastasis is greater in SCC. About one third of mucosal or lingual lesions will have metastasized before diagnosis. An SCC may develop in normal tissue or in preexisting actinic keratosis or a patch of leukoplakia.

Malignant Melanoma

Incidence and Mortality

Although it is the least common of the major skin cancers, MM is the most lethal. Malignant melanoma is the leading cause of death from diseases of the skin, and it is responsible for about 74 percent of all deaths from cutaneous cancers. The mortality rate for MM is increasing faster than that for any other cancer except lung cancer. Not unexpectedly, the incidence of the disease is rising too: at the rate of three to four percent per year. The lifetime probability of developing MM is 0.6 to two percent. If current trends continue, by the year 2000, one in 90 people will fall victim to MM during their lifetimes.

In women, the frequency of MM is second only to lung cancer. Females have a greater risk of developing MM at a younger age, while men are more likely to develop MM when they are older (male/female age-adjusted incidence ratio = 1.2). However, the overall incidence of MM increases with age, with 75 percent of cases occurring in people over the age of 40.

Risk Factors

Increased risk for developing MM is associated with the presence of dysplastic nevi. Dysplastic nevi tend to be atypical in appearance, larger than characteristic moles, and uneven in color. Dysplastic nevi are both potential precursors of MM and markers for increased risk of developing MM. The four percent of the population with dysplastic nevi have about a six percent risk of developing MM, versus one percent in the general population. For persons with dysplastic nevi and a personal or family history of MM, the risk is higher. About 100,000 people in the United States have dysplastic nevi and two family members who have had MM. For these individuals, the risk approaches 100 percent.

Other factors related to elevated risk for MM include hormonal changes during a woman's lifetime. During pregnancy, menopause, and estrogen replacement therapy, a woman has a statistically greater likelihood of developing melanoma. The immunocompromised status of AIDS patients also places them at a greater risk for MM.

Although many MMs arise from pigmented moles, more than half occur in melanocytes in normal skin. Lesions most often appear on the trunk in men and on the leg in women, but MM can also occur elsewhere on the body and in mucous membranes, the eye, and the central nervous system where pigmented cells occur. Melanomas vary in size, shape, and color, but most are pigmented.

Malignant melanomas are seldom seen in children. Occasionally, however, MM develops in congenital nevi. All congenital nevi are predisposed toward malignant change, but the malignant potential seems to be related to size. Giant congenital nevi are more likely to develop malignancy than other smaller, congenital nevi.