Melanoma, Malignant
A neoplasm that arises from melanocytes, malignant melanoma is potentially the most lethal of the skin cancers. It accounts for 3% to 4% of all cancers, and its incidence is rapidly increasing. Melanoma is slightly more common in females than in males and is unusual in children. Peak incidence occurs between ages 50 and 70, although the incidence in younger age groups is increasing.
Melanoma spreads through the lymphatic and vascular systems and metastasizes to the regional lymph nodes, skin, liver, lungs, and central nervous system (CNS). Its course is unpredictable, however, and recurrence and metastases may not appear for more than 5 years after resection of the primary lesion. The prognosis varies with the tumor thickness. In most patients, superficial lesions are curable, whereas deeper lesions tend to metastasize.
Common sites for melanoma are the head and neck in males, the legs in females, and the backs of people exposed to excessive sunlight. Up to 70% of malignant melanomas arise from a preexisting nevus.
The four types of melanoma are:
Superficial spreading melanoma, the most common type (accounting for 50% to 70% of cases), usually develops between ages 40 and 50.
Nodular melanoma usually develops between ages 40 and 50 and accounts for 12% to 30% of cases. It grows vertically, invades the dermis, and metastasizes early.
Acral-lentiginous melanoma is the most common melanoma among Hispanics, Asians, and Blacks. It occurs on the palms and soles and in sublingual locations.
Lentigo maligna melanoma is relatively rare, accounting for 4% to 10% of cases. This is the most benign, the slowest growing, and the least aggressive of the four types. It most commonly occurs in areas heavily exposed to the sun. It arises from a lentigo maligna on an exposed skin surface
and usually occurs between ages 60 and 70.
Causes
Several factors may influence the development of melanoma.
Excessive exposure to sunlight—Melanoma occurs most commonly in those who live in sunny, warm areas and often develops on body parts that are exposed to the sun.
Skin type—Most people who develop melanoma are of Celtic or Scandinavian ancestry, are prone to sunburn, and have blond or red hair, fair skin, and blue eyes. Melanoma is rare among blacks; when it does develop, it usually arises in lightly pigmented areas (the palms, plantar surface of the feet, or mucous membranes).
Genetic factors—Familial atypical multiple mole melanoma syndrome is characterized by multiple dysplastic nevi; it carries an extremely high lifetime risk of melanoma.
Family history—Melanoma occurs slightly more often within families.
Past history of melanoma—A person who has had one melanoma is at greater risk for developing a second.
Complications
This cancer has a strong tendency to metastasize; complications result from disease progression to the lungs, liver, or brain.
Assessment
The patient’s history may include a sore that doesn’t heal, a persistent lump or swelling, and changes in preexisting skin markings, such as moles, birthmarks, scars, freckles, or warts. Suspect melanoma when any preexisting skin lesion or nevus enlarges, changes color, becomes inflamed or sore, itches, ulcerates, bleeds, changes texture, or shows signs of surrounding pigment regression.
In superficial spreading melanoma, inspection may reveal lesions on the ankles or the inside surfaces of the knees. These lesions may appear red, white, or blue over a brown or black background. They may have an irregular, notched margin. Palpation may reveal small, elevated tumor nodules that may ulcerate and bleed. These tumors may grow horizontally for years, but when vertical growth occurs, the prognosis worsens.
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