– Skin cancers can be divided into two groups: melanomas and nonmelanomas. Three distinct types of nevi (moles) give rise to melanomas: common acquired, dysplastic, and congenital melanocytic; they produce four types of melanoma: superficial spreading (70%), nodular (15%), lentigomaligna (less than 10%), and acrolentiginous (less than 5%). Nonmelanomas are typically either basal cell or squamous cell in origin.
Causes and Incidence
Environmental factors such as ultraviolet radiation and chronic sun exposure are strongly linked to the development of skin cancer. Long-term x-ray exposure and occupational exposure to radium, arsenic, coal tar, and creosote are also risk factors. Genetic risk factors such as a fair complexion, light hair, and difficulty tanning play a role, as does family history.
Skin cancer is the most common of all malignancies. An estimated 600,000 cases are diagnosed annually in the United States alone. Most are nonmelanomas, but more than 32,000 are melanomas, and the incidence of melanoma is increasing by 4% a year. Fair-skinned individuals over 40 years of age who live near the equator and have a history of long-term sun exposure are at highest risk.
Basal cell carcinomas vary considerably in appearance but usually begin as a small, shiny, flesh-colored nodule on the skin. The carcinoma enlarges slowly and develops a pearly border with telangiectases on the surface. It often bleeds, crusts, and then rebleeds in a chronic cycle. It rarely metastasizes but does invade adjacent tissue structures. Squamous cell carcinomas are usually scaly and crusty or nodular, warty, and raised and often develop in keratotic tissue or old scars. They eventually ulcerate and invade the underlying tissue. They rarely metastasize, but when they do, the lungs are the most common site. Malignant melanomas arise from a mole that begins to show changes in size, color, shape, and consistency. They begin by growing on the epidermis and then invade the dermis and subcutaneous tissues. Once this occurs, the tumor metastasizes fairly rapidly through the vascular and lymphatic systems. Common metastatic sites include the bones, brain, liver, and lungs.
A skin lesion that does not go away and that grows larger over time or a mole that changes appearance is a possible sign, as are itchiness, scaling, oozing, bleeding from a mole or lesion, and changes in sensation.
The prognosis is excellent with intervention, particularly with nonmelanoma carcinomas, because metastasis is rare. The long-term prognosis for melanomas is tied to the thickness of the tumor at the time of diagnosis. Tumors over 3 mm deep carry a survival rate of less than 50%. Metastasized disease reduces the survival rate dramatically. Common complications include scarring and disfigurement at the site of tumor removal.
Tissue biopsy and a histologic examination form the base for definitive diagnosis.
Excision is the treatment of choice for melanoma; excision, cryosurgery, electrodesiccation and curettage, and Mohs chemosurgery are used for nonmelanomas.
Topical chemotherapeutic agents to treat premalignant actinic keratosis; interferon to treat recurrent or advanced basal cell carcinoma; hyperthermic regional perfusions in combination with surgery to treat melanomas.
Radiation in combination with surgery for extensive nonmelanomas; radiation may be used instead of surgery in elderly patients or to treat nonmelanomatous lesions of the nose, eyelids, or lips (melanomas are radioresistant); prevention education about sun exposure and use of sun screens and protective clothing when in the sun.