Malignant Melanoma

Introduction: 

Incidence of malignant melanoma, a neoplasm that arises from melanocytes, has increased by 50% in the past 20 years. In particular, an increase in incidence of melanoma in situ suggests earlier detection. The disorder varies in different populations but is about 10 times more common in white than in nonwhite populations. 

The four types of melanomas are 

1. superficial spreading melanoma, 
2. nodular malignant melanoma, 
3. lentigo maligna melanoma, and 
4. acral-lentiginous melanoma.

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 metastasis may occur more than 5 years after resection of the primary lesion. If it spreads to regional lymph nodes, the patient has a 50% chance of survival.
The prognosis varies with tumor thickness. Generally, superficial lesions are curable, whereas deeper lesions tend to metastasize. The Breslow Level Method measures tumor depth from the granular level of the epidermis to the deepest melanoma cell. Melanoma lesions less than 0.76 mm deep have an excellent prognosis, whereas deeper lesions (more than 0.76 mm deep) are at risk for metastasis. The prognosis is better for a tumor on an extremity (which is drained by one lymphatic network) than for one on the head, neck, or trunk (which is drained by several networks).

Causes & Risk Factors
Several factors may influence the development of melanoma:

• Excessive exposure to ultraviolet light. Melanoma is most common in sunny, warm areas and commonly develops on parts of the body that are exposed to the sun. A person who has a blistering sunburn before age 20 has twice the risk of developing melanoma.
• Skin type. Most persons who develop melanoma have blond or red hair, fair skin, and blue eyes; are prone to sunburn; and are of Celtic or Scandinavian descent. 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).
• Autoimmune factors. Genetic and autoimmune effects may be causes.
• Hormonal factors. Pregnancy may increase risk and exacerbate growth.
• Family history. A person with a family history of melanoma has eight times the risk of developing the disorder.
• History of melanoma. A person who has had one melanoma has 10 times the risk of developing a second.

Clinical Manifestations
Common sites for melanoma are on the head and neck in men, on the legs in women, and on the backs of people exposed to excessive sunlight. Up to 70% arise from a preexisting nevus. They rarely appear in the conjunctiva, choroid, pharynx, mouth, vagina, or anus.

Suspect melanoma by using the ABCD Rule of Melanoma:

• Asymmetry of borders
• Bleeding or crusting
• Color blue/black or variegated
• Diameter greater than 2¼? (5.7 cm).

Each type of melanoma has special characteristics:

Superficial spreading melanoma arises on chronically sun-exposed areas, such as the legs and upper back. Characteristically, it has a red, white, and blue color over a brown or black background and an irregular, notched margin. Its surface is irregular, with small, elevated tumor nodules that may ulcerate and bleed. Horizontal growth may continue for many years; when vertical growth begins, the prognosis worsens.

Nodular malignant melanoma occurs more commonly in men and can be located anywhere on the body. It’s the most frequently misdiagnosed melanoma because it resembles a blood blister or polyp.

Lentigo maligna melanoma commonly develops under the fingernails, on the face, and on the backs of the hands. This lesion looks like a large (1? to 2? [2.5- to 5-cm]), flat freckle of tan, brown, black, whitish, or slate color, and has irregularly scattered black nodules on the surface. It develops slowly, usually over many years, and eventually may ulcerate.

Acral-lentiginous melanoma is more common in Asian and Black individuals.

Diagnosis
A skin biopsy with histologic examination can distinguish malignant melanoma from a benign nevus, seborrheic keratosis, and pigmented basal cell epithelioma; it can also determine tumor thickness. Physical examination, paying particular attention to lymph nodes, can point to metastatic involvement.
Baseline laboratory studies include a complete blood count with differential, erythrocyte sedimentation rate, platelet count, liver function studies, and urinalysis. Depending on the depth of tumor invasion and metastasis, baseline diagnostic studies may also include a chest X-ray and computed tomography (CT) scan of the chest and abdomen. Signs of bone metastasis may call for a bone scan; CNS metastasis, a CT scan of the brain.

Treatment
A patient with malignant melanoma requires surgical resection to remove the tumor. The extent of resection depends on the size and location of the primary lesion. Closure of a wide resection may require a skin graft. Surgical treatment may also include regional lymphadenectomy. Cutaneous melanoma is nearly 100% curable by excision if diagnosed when malignant cells are confined to the epidermis.
Deep primary lesions may merit adjuvant chemotherapy and biotherapy or immunotherapy to eliminate or reduce the number of tumor cells. Radiation therapy is usually reserved for metastatic disease; gene therapy may also be a treatment option.
Regardless of the treatment method, melanomas require close, long-term follow-up to detect metastasis and recurrences.