What Is Melanoma?
One of the most dangerous forms of skin cancer, melanoma may appear on normal skin or could begin as a mole that alters in appearance. Over 90 percent of melanomas are caused by mutations in the DNA of skin cells called melanocytes (which produce the pigment melanin). Melanomas starting on the skin are called cutaneous melanomas. Less commonly, melanoma can originate in other locations such as the eyes (ocular or uveal melanoma) or lining surfaces such as the sinuses or vaginal tract (mucosal melanoma).
There are approximately 75,000 new cases of melanoma diagnosed and 9,000 melanoma related deaths in the United States each year. Unfortunately the incidence is increasing. The median age of diagnosis is 59 years, but people of all ages can develop melanoma.
Risk Factors for Melanoma
There are several risk factors for developing cutaneous melanoma, including the following:
- Personal history of melanoma
- Family history of melanoma
- Multiple atypical moles or dysplastic nevi
- Fair skin
- Sun exposure
- Certain inherited mutations in the DNA in a very small subset of melanomas
Signs of Melanoma
A skin lesion may be cancerous if it exhibits certain telltale characteristics, including the following
- Uneven shape
- Ragged edges
- Uneven coloration
- Changes in size
- Changes in texture
Types of Melanoma
Cutaneous melanomas were traditionally sub-classified based on histology (how the cells that make up the melanoma appear under the microscope).
Specific types of cutaneous melanomas include superficial spreading melanoma, nodular melanoma, acral melanoma, and lentigo maligna melanoma. Approximately 70 percent of cases are superficial spreading, which can grow on the surface of the skin (radial phase) for several years before growing downward (vertical phase). Common locations include the back and, in women, on the legs. Nodular melanomas comprise approximately 10-15 percent of melanomas and lack a radial growth phase but rather grow downward vertically and tend to develop in the elderly with a mean age of presentation of 69 years. They often develop on the head, neck, and back of the hands. They appear flat and can grow over a broad area as a radial growth phase over many years.
Stages of Melanoma
Melanomas are staged as follows:
- Melanoma in situ: Has not invaded the lower layers of skin
- Stage I: Detected at the primary site (starting spot on the skin) only
- Stage II: Detected at the primary site (starting spot on the skin) only
- Stage III: Spread to the draining lymph nodes or along the lymph channels on the way to the lymph nodes (in-transit metastases)
- Stage IV: Spread distantly in the body either by the blood or the lymph system
The following features of melanoma (as described in a pathology report) affect staging:
- The Breslow thickness: The depth of the invasion into the skin of the melanoma. A thin melanoma is < 1 mm in depth. A deep melanoma is over 4 mm in depth. An intermediate depth melanoma is between 1-4 mm. The deeper the melanoma the worse the prognosis
- Ulceration: The presence of ulceration may increase the stage.
- Mitoses (dividing cells): The presence of mitoses can increase the stage of thin melanomas and may be associated with worse disease-specific survival.
Treatments for Melanoma
Treatments for melanoma include the following procedures and FDA-approved medications
- Procedures include wide excision, sentinel lymph node biopsy, and completion lymph node dissection.
- Medications include chemotherapies and immune therapies for stage II, III, and IV melanomas.