Melanoma accounts for only 5% of all skin cancers, yet it results in most of the skin cancer deaths, according to the American Cancer Society. About 62,720 new cases of melanoma were diagnosed in the United States during 2009.
At first, melanoma cells are found in the epidermis and top layers of the dermis. However, once they grow downward into the dermis, the cancer can come into contact with lymph and blood vessels, and from there spread to other parts of the body. The thicker the melanoma, the greater the likelihood that it could spread to distant sites.
Removing the lesion before it reaches the deeper layers of the skin is important to achieve a cure.
Superficial Spreading Melanoma. Superficial spreading melanoma is the most common and most curable type of melanoma. It is flat, asymmetrical, unevenly colored, and usually grows outward across the surface of the skin. Superficial spreading melanoma accounts for about 70% of melanomas. In men, it occurs most often on the back. In women, it is most likely to be seen on the back of the leg.
Nodular Melanoma. Nodular melanoma appears as a fast-growing brown or black lump, and its characteristics do not always fit the definitions described above. It is important to check for this type of melanoma because it is associated with an outbreak of other tumors. Nodular melanoma accounts for about 5% of melanomas. It is usually seen on the trunk or limbs.
Lentigo Maligna. Lentigo maligna (sometimes called Hutchinson's freckle) usually occurs in elderly people and is marked by flat, mottled, tan-to-brown freckle-like spots with irregular borders. These lesions often appear on the face or other sun-exposed areas and typically grow slowly for 5 - 15 years before cancer appears. Lentigo maligna melanoma accounts for 4 - 15% of melanoma cases.
Acral Lentiginous Melanoma. Although rare, acral lentiginous melanoma is the most common melanoma among African and Asian populations. It commonly appears as a dark patch on the palms, soles, fingers, or toes, under fingernails or toenails, or in mucus membranes.
Several unusual types of melanomas exist, but they are relatively uncommon.
Melanoma cells usually spread first through the lymph vessels or glands. Melanoma cells can also spread by way of blood vessels to various organs, carrying cancer to the liver, lungs, brain, or other sites.
Melanomas tend to grow in stages:
Review Date: 07/04/2010
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.