Melanoma

Overview

Melanoma is a potentially lethal form of skin cancer that originates in melanocytes - cells in the epidermis that produce skin pigment (melanin). Cancer cells are called malignant because they multiply uncontrollably and form destructive growths (tumors).

Melanoma is the most aggressive form of skin cancer and the most likely type to spread (metastasize) to distant organs. Small, early melanomas are highly curable, but advanced metastatic disease is often fatal.

In the United States, the incidence of melanoma is substantially increasing in both men and women. Melanoma usually occurs in adults and less commonly in children or adolescents; however, tanning and sunburns during childhood and adolescence markedly increase a person’s risk of developing melanoma later in life.

Causes and Risk Factors

Illustrated skin cross-section showing epidermis, dermis and subcutis

Exposure to ultraviolet radiation from the sun and tanning beds is the primary cause of melanoma. Individuals with fair skin have a higher risk for melanoma, but the disease can also arise in people with dark skin.

Melanoma can occur spontaneously or arise in an existing mole that changes in size and appearance. Melanoma may develop in any place in the body where melanocytes exist, including the eyes and digestive tract.

Risk Factors For Melanoma:

  • Sun exposure
  • Severe, blistering sunburns in childhood or adolescence
  • Light-colored skin, blond hair, red hair, or light-colored eyes
  • The presence of large moles, numerous moles, or unusual moles
  • Family history of melanoma
  • Weakened immune system
  • Exposure to radiation
  • Exposure to industrial chemicals such as solvents or vinyl chloride.

Symptoms

In women, melanoma most often occurs on the arms or legs; in men the condition often develops on the trunk, head, or neck. The most common signs of melanoma are unusual changes in the size, shape, or color of a mole, including darkening, discoloration, itching, enlargement, and bleeding.Pictures illustrate the ABCD rules for melanoma identification

ABCDE, a mnemonic for early signs of melanoma in a mole, stands for:

  • Asymmetry (one half of the mole is different from the other)
  • Border irregularity (ragged or blurred edges)
  • Color lacks uniformity (multiple colors are present, including black, black-blue, brown, and tan)
  • Diameter greater than 6 millimeters
  • Evolving or changing appearance.

Satellite moles, new moles that develop close to a pre-existing mole, often occur with melanoma. Bleeding and ulceration of an abnormal mole are late signs of the disease.

Diagnosis

Early melanoma is often extremely difficult to distinguish from benign pigmented moles. Suspicious lesions must be biopsied in a procedure that involves cutting out the abnormal tissue and a portion of surrounding normal tissue for examination under a microscope.

The extent (stage) of the disease determines a patient's treatment, prognosis, and likelihood of recurrence. The stage is determined by:

  • Thickness of the tumor
  • Whether the skin lesion is bleeding or ulcerated
  • Whether there is lymph node involvement
  • Whether the cancer has metastasized to distant sites.

Early stage melanoma is highly curable; however, more advanced stages are more difficult to treat. Metastatic melanoma, which most commonly spreads to the liver and lungs, has a high mortality rate.

For staging purposes, computed tomography (CT) provides a series of detailed images of various organs and tissues to detect metastases. Positron emission tomography scan (PET scan) may show evidence of tumor cells at distant sites in the body. Magnetic resonance imaging (MRI) may also be obtained to provide additional images.

Treatment

  • Surgical excision is the primary treatment for thin, early-stage melanomas, which are highly curable.
  • Surgical excision and a biopsy of the sentinel lymph node (the first node affected by the cancer) are performed for thicker melanomas.
  • When cancer involves the sentinel lymph node, a more extensive removal of numerous lymph nodes is required.
  • Chemotherapy, which uses medications to destroy cancer cells, is required for more advanced melanoma that has spread beyond the skin. Chemotherapy is often administered after surgery to destroy any remaining cancer cells and decrease the risk of recurrence.
  • Radiation therapy may also be required to destroy remaining cancer cells.
  • Immunotherapy involves drugs that stimulate the body’s immune system to defend itself against cancer.
  • Targeted therapy uses treatments that attack specific types of cancer cells without damaging normal tissues.

Prevention

Sun exposure is the primary preventable risk factor for melanoma. The skin should be protected by the avoidance of sun exposure between 10 am and 3 pm (the hours of highest ultraviolet radiation intensity). Sunscreen with sun protection factor (SPF) 30 or higher should be applied to exposed skin. Sunglasses, wide-brimmed hats, and protective clothing also provide essential skin protection. Children must be protected from sunburns to decrease their risk of developing melanoma in adulthood, and tanning beds should be avoided.

Early Detection

Self-examination of the skin can detect early signs of melanoma, such as new skin lesions or changes in the size, shape, and color of existing moles. A physician should evaluate any suspicious skin lesions. Individuals with risk factors for skin cancer should undergo an annual complete skin examination by a physician.

Sources

  • Melanoma Treatment. National Cancer Institute at the National Institutes of Health website. http://www.cancer.gov/cancertopics/pdq/treatment/melanoma/HealthProfessional. Accessed May 29, 2014.
  • American Cancer Society: Cancer Facts And Figures 2014. American Cancer Society website. http://www.cancer.org/acs/groups/content/@research/documents/webcontent/acspc-042151.pdf. Accessed May 29, 2014.
  • Melanoma. American Academy of Dermatology website. http://www.aad.org/media-resources/stats-and-facts/conditions/melanoma. Accessed May 29, 2014.
  • The Facts About Melanoma. Cleveland Clinic website. http://my.clevelandclinic.org/disorders/skin_cancer/hic_the_facts_about_melanoma.aspx. Accessed May 30, 2014.