Melanoma is a malignant tumor of melanocytes, which are the cells that make the pigment melanin and are derived from the neural crest. Although most melanomas arise in the skin, they may also arise from mucosal surfaces or at other sites to which neural crest cells migrate, including the uveal tract. Uveal melanomas differ significantly from cutaneous melanoma in incidence, prognostic factors, molecular characteristics, and treatment. (Refer to the PDQ summary on Intraocular (Uveal) Melanoma Treatment for more information.)
Incidence and Mortality
Estimated new cases and deaths from melanoma in the United States in 2014:
- New cases: 76,100.
- Deaths: 9,710.
Skin cancer is the most common malignancy diagnosed in the United States, with 3.5 million cancers diagnosed in 2 million people annually. Melanoma represents less than 5% of skin cancers but results in most deaths.[1,2] The incidence has been increasing over the past four decades. Elderly men are at highest risk; however, melanoma is the most common cancer in young adults aged 25 to 29 years and the second most common cancer in those aged 15 to 29 years. Ocular melanoma is the most common cancer of the eye, with approximately 2,000 cases diagnosed annually.
Risk factors for melanoma include both intrinsic (genetic and phenotype) and extrinsic (environmental or exposure) factors:
- Sun exposure.
- Pigmentary characteristics.
- Multiple nevi.
- Family and personal history of melanoma.
- Environmental exposures.
(Refer to the PDQ summaries on Skin Cancer Prevention and the Genetics of Skin Cancer for more information about risk factors.)
Schematic representation of normal skin. Melanocytes are also present in normal skin and serve as the source cell for melanoma. The relatively avascular epidermis houses both basal cell keratinocytes and squamous epithelial keratinocytes, the source cells for basal cell carcinoma and squamous cell carcinoma, respectively. The separation between epidermis and dermis occurs at the basement membrane zone, located just inferior to the basal cell keratinocytes.
Refer to the PDQ summary on Skin Cancer Screening for more information.
Melanoma occurs predominantly in adults, and more than 50% of the cases arise in apparently normal areas of the skin. Although melanoma can occur anywhere, including on mucosal surfaces and the uvea, melanoma in women occurs more commonly on the extremities, and in men it occurs most commonly on the trunk or head and neck.
Early signs in a nevus that would suggest a malignant change include the following:
- Darker or variable discoloration.
- An increase in size or the development of satellites.
- Ulceration or bleeding (later signs).