General Information About Melanoma
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 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).
A biopsy, preferably by local excision, should be performed for any suspicious lesions. Suspicious lesions should never be shaved off or cauterized. The specimens should be examined by an experienced pathologist to allow for microstaging.
Studies show that distinguishing between benign pigmented lesions and early melanomas can be difficult, and even experienced dermatopathologists can have differing opinions. To reduce the possibility of misdiagnosis for an individual patient, a second review by an independent qualified pathologist should be considered.[5,6] Agreement between pathologists in the histologic diagnosis of melanomas and benign pigmented lesions has been studied and found to be considerably variable.[5,6]
Evidence (discordance in histologic evaluation):
- One study found that there was discordance on the diagnosis of melanoma versus benign lesions in 37 of 140 cases examined by a panel of experienced dermatopathologists. For the histologic classification of cutaneous melanoma, the highest concordance was attained for Breslow thickness and presence of ulceration, while the agreement was poor for other histologic features such as Clark level of invasion, presence of regression, and lymphocytic infiltration.
- In another study, 38% of cases examined by a panel of expert pathologists had two or more discordant interpretations.
Prognosis is affected by the characteristics of primary and metastatic tumors. The most important prognostic factors have been incorporated into the revised 2009 American Joint Committee on Cancer staging and include the following:[4,7-9]
- Thickness and/or level of invasion of the melanoma.
- Mitotic index, defined as mitoses per millimeter.
- Ulceration or bleeding at the primary site.
- Number of regional lymph nodes involved, with distinction of macrometastasis and micrometastasis.
- Systemic metastasis.
- Site—nonvisceral versus lung versus all other visceral sites.
- Elevated serum lactate dehydrogenase level.
Microscopic satellites, recorded as present or absent, in stage I melanoma may be a poor prognostic histologic factor, but this is controversial. The presence of tumor infiltrating lymphocytes, which may be categorized as brisk, nonbrisk, or absent, is under study as a potential prognostic factor.
Other PDQ summaries containing information related to melanoma include the following:
- American Cancer Society: Cancer Facts and Figures 2014. Atlanta, Ga: American Cancer Society, 2014. Available online. Last accessed November 24, 2014.
- Melanoma. Bethesda, Md: National Library of Medicine, 2012. Available online. Last accessed May 15, 2014.
- Bleyer A, O’Leary M, Barr R, et al., eds.: Cancer Epidemiology in Older Adolescents and Young Adults 15 to 29 Years of Age, Including SEER Incidence and Survival: 1975-2000. Bethesda, Md: National Cancer Institute, 2006. NIH Pub. No. 06-5767. Also available online. Last accessed October 29, 2014.
- Slingluff CI Jr, Flaherty K, Rosenberg SA, et al.: Cutaneous melanoma. In: DeVita VT Jr, Lawrence TS, Rosenberg SA: Cancer: Principles and Practice of Oncology. 9th ed. Philadelphia, Pa: Lippincott Williams & Wilkins, 2011, pp 1643-91.
- Corona R, Mele A, Amini M, et al.: Interobserver variability on the histopathologic diagnosis of cutaneous melanoma and other pigmented skin lesions. J Clin Oncol 14 (4): 1218-23, 1996. [PUBMED Abstract]
- Farmer ER, Gonin R, Hanna MP: Discordance in the histopathologic diagnosis of melanoma and melanocytic nevi between expert pathologists. Hum Pathol 27 (6): 528-31, 1996. [PUBMED Abstract]
- Balch CM, Soong S, Ross MI, et al.: Long-term results of a multi-institutional randomized trial comparing prognostic factors and surgical results for intermediate thickness melanomas (1.0 to 4.0 mm). Intergroup Melanoma Surgical Trial. Ann Surg Oncol 7 (2): 87-97, 2000. [PUBMED Abstract]
- Manola J, Atkins M, Ibrahim J, et al.: Prognostic factors in metastatic melanoma: a pooled analysis of Eastern Cooperative Oncology Group trials. J Clin Oncol 18 (22): 3782-93, 2000. [PUBMED Abstract]
- Balch CM, Gershenwald JE, Soong SJ, et al.: Final version of 2009 AJCC melanoma staging and classification. J Clin Oncol 27 (36): 6199-206, 2009. [PUBMED Abstract]
- León P, Daly JM, Synnestvedt M, et al.: The prognostic implications of microscopic satellites in patients with clinical stage I melanoma. Arch Surg 126 (12): 1461-8, 1991. [PUBMED Abstract]
- Mihm MC Jr, Clemente CG, Cascinelli N: Tumor infiltrating lymphocytes in lymph node melanoma metastases: a histopathologic prognostic indicator and an expression of local immune response. Lab Invest 74 (1): 43-7, 1996. [PUBMED Abstract]
- Shen P, Guenther JM, Wanek LA, et al.: Can elective lymph node dissection decrease the frequency and mortality rate of late melanoma recurrences? Ann Surg Oncol 7 (2): 114-9, 2000. [PUBMED Abstract]
- Tsao H, Cosimi AB, Sober AJ: Ultra-late recurrence (15 years or longer) of cutaneous melanoma. Cancer 79 (12): 2361-70, 1997. [PUBMED Abstract]