What are the Types of Melanoma?
Melanoma is a type of cancer that develops in the melanocytes—the cells in our skin that produce pigment. Cutaneous or skin melanoma (also called malignant melanoma, although any diagnosis of melanoma is cancer even if “malignant” is not used) occurs when these cancerous cells grow out of control (mutate) and crowd out normal cells. Usually, cutaneous melanoma begins in the top layer of the skin—the epidermis—and can become invasive from there. When the term melanoma is used, it is generally referring to cutaneous melanoma, because the vast majority of melanomas are of the skin.
There are four main subtypes of cutaneous melanoma: superficial spreading; nodular; lentigo maligna; and acral lentiginous. Other subtypes, such as desmoplastic and amelanotic melanoma, also exist but are rare.
The incidence of cutaneous melanoma appears to be on a steady rise throughout the world due to increased ultraviolet exposure from the sun and the use of tanning beds. In the U.S., the rates of melanoma have been rising for the last 30 years.
In 2020, an estimated 100,350 adults (60,190 men and 40,160 women) in the United States will be diagnosed with invasive cutaneous melanoma—melanoma that penetrates the skin’s second layer (the dermis). It is estimated that over 7,000 people in the U.S. died of melanoma in 2019.
Besides cutaneous melanoma, there are four other general kinds of melanoma, all of which are less common than cutaneous melanoma.
Ocular melanoma and mucosal melanoma are types of non-cutaneous melanoma that develop in the eye and mucosal linings of the body (such as the mouth or inside the nose), respectively.
Melanoma with an unknown primary (MUP) is the name given to melanomas that have spread (metastasized) to internal sites in the body, but the original or “primary” tumor site is unknown.
Finally, all melanomas that occur in children are generally grouped together as pediatric melanoma.
After cutaneous, the second most common type of melanoma is ocular melanoma. Just as in cutaneous melanoma, ocular melanoma develops when melanocytes become cancerous and mutate, but instead of being on the skin, these melanocytes are in and around the eye. Read more about ocular melanoma here.
Mucosal melanomas develop in the mucous membranes, such the sinuses, nasal passages, oral cavity, vagina, and anus. Mucosal tissues contain melanocytes just as skin does, and those melanocytes can become cancerous. Mucosal melanomas are rare, accounting for only about one percent of all cases of melanoma, but they tend to be more aggressive and have less favorable prognoses compared to cutaneous melanoma. There is currently no standard for staging or treating mucosal melanoma. Researchers have not been able to identify any risk factors: Neither UV exposure nor family history seems to play a role. Read more about mucosal melanoma here.
Melanomas With Unknown Primary (MUP)
In rare cases, melanoma is found to have spread to lymph nodes or organs, but the original tumor site is unknown. When this type of melanoma occurs, it is called melanoma of unknown primary (MUP). Only about 3% of melanomas are MUP.
Current hypotheses suggest that most of these melanomas originate on the skin and arise from:
- Melanomas of the skin that were incompletely removed
- “Regressed” melanomas: When your body’s immune system may have destroyed a portion of the cancerous cells in a cutaneous melanoma but not before some melanoma cells were able to get into lymph nodes or blood vessels
- Pigmented cells that traveled to the lymph nodes and were transformed into melanoma.
Pediatric melanoma is rare. According to the National Cancer Institute, about 400 individuals under 20 years old are diagnosed with melanoma each year. Pediatric melanoma is defined as melanoma occurring in patients younger than 18 years, so we can assume the number of pediatric melanoma cases diagnosed each year is slightly less than 400. As in adults, the most common type of melanoma in children is cutaneous melanoma. Pediatric melanoma that is diagnosed before age 10 is different from melanoma in adults, and melanoma diagnosed after age 10 is very similar to that in adults. Read more about pediatric melanoma here.