While most melanomas occur on the skin, a small percentage of these dangerous cancers are found in other parts of the body. These non-skin melanomas also are called noncutaneous melanomas.
In addition to being rare, noncutaneous melanomas often are aggressive and difficult to treat. Answering questions about this rare cancer is Kevin Kim, M.D., associate professor in MD Anderson's Department of Melanoma Medical Oncology.
What is melanoma?
Melanoma is an aggressive type of cancer that usually shows up as a pigmented growth on the skin. However, less common types may be found in other areas.
What causes non-skin melanoma?
Melanoma originates in melanocytes. These are cells in the body that make melanin, the substance that gives skin pigment or color. They are located in many places throughout the body, not just the skin. Considerable numbers of melanocytes are in the digestive and urogenital tracts and mucous glands.
Non-skin melanomas are not known to be caused by sun damage, exposure to ultraviolet rays, family history or moles.
Besides the skin, where do melanomas develop?
Melanomas may occur in any organ or part of the body with melanin-containing cells (melanocytes).
There are four main types of noncutaneous melanomas:
Mucosal (of the mucous membranes)
Anal or rectal
How common are non-skin melanomas?
About 4% to 5% of primary melanomas are noncutaneous.
Ocular: This is the most common site of non-skin melanomas, and 80% of noncutaneous melanomas occur in the eye. Melanoma of the eye is the most common type of eye cancer in adult Caucasians and is eight times more common in this group than in African-Americans. About 2,000 cases are reported each year in the United States and Canada.
Mucosal: These rare tumors make up about 1% of all melanomas. However, vulvar melanoma is the second most common cancer of the vulva. While vaginal melanoma makes up less than 10% of genital tract melanomas in women, it is extremely aggressive. Anus/rectum is the most common mucosal site for noncutaneous melanoma.
Can melanomas metastasize?
Yes. Melanoma, including melanoma of the skin, can spread to several sites, including lymph nodes, bone, lung, liver, spleen and kidneys.
Melanoma tumors of the eye may be:
Low-grade, slow growing and unlikely to spread
High-grade, fast growing and early to spread
What are the symptoms of non-skin melanomas?
Symptoms vary according to where the melanoma is located.
Eye: Visual disturbance, mass, variable pigmentation, distortion of the pupil
Nose or nasal sinuses: Mass, nosebleed, discharge from nose, protruding eyes
Anal or rectal: Mass, bleeding from the rectum, weight loss, painful defecation
Metastasized to the liver: Mass, abdominal pain
Metastasized to lymph nodes: Lymph node enlargement
How are noncutaneous melanomas diagnosed?
Non-skin melanomas often are challenging to diagnose. They often are discovered during medical evaluation for specific symptoms. Ocular melanomas are usually found during detailed eye examination by an ophthalmologist; vaginal melanomas during pelvic examinations; and anorectal melanomas during scope examination of the anus and rectum. Unfortunately, there are no reliable blood tests to diagnose melanoma.
What are the risk factors for non-skin melanoma?
Generally, melanocytes throughout the body increase as people get older. All types of melanoma are more common in people over 50.
People who have had a prior melanoma (skin or non-skin) are at risk of the cancer spreading.
People with moles or freckles on their skin or moles on the iris of the eye may be at increased risk for a certain type of eye melanoma.
Anorectal melanoma is found most frequently in AIDS patients.
Why are non-skin melanomas so dangerous?
Non-skin melanomas often are in advanced stages when they are diagnosed. Because they are so rare, they often are not suspected initially. Because of the rich vascular network and lymphatic supply of many of the areas in which they occur, they often spread quickly. In addition, the biology of non-skin melanomas is different than the biology of more frequent skin melanomas, which may explain the poorer prognosis in patients with non-skin melanomas. For example, mucosal melanomas tend to contain a genetic mutation in a gene called c-kit, and ocular melanomas are more likely to contain a mutation in gnaq gene, while skin melanomas frequently harbor mutations in different genes, such as braf or nras.
What should I do if I'm at risk or think I may have a non-skin melanoma?
See your doctor if you notice:
Discoloration in your eyes or changes in vision
New growths or non-healing sores in your mouth
Rectal bleeding, pain during defecation, worsening symptoms of hemorrhoids
Unexplained vaginal bleeding
Women should have annual gynecological exams and be sure they include examinations of the external genitalia.
What is the treatment for non-skin melanoma?
Treatment for non-skin melanoma may include surgery, chemotherapy, radiation, other treatment methods or a combination of treatments. Treatment choices depend on the size and type of the tumor and its location.
Are new treatments being studied for melanoma?
Much research is being done on treatments for melanoma, including vaccines and drugs that target specific growth pathways in the tumor.