Melanoma Types

While all melanomas evolve from a single type of cell, the melanocyte, melanoma is further divided into four sub-types each with their own prognosis and rate of metastasis. The four sub-types are classified according to their radial and vertical growth patterns. Radial growth indicates how aggressively the skin cancer has spread across the skin. Vertical growth indicates how far into the skin the cancer has spread.

Superficial Spreading Melanoma (SSM)

Superficial spreading melanoma is the most common variety, accounting for over two thirds of all diagnosed cases. The skin cancer spreads radially at first, and spreads slowly. Once SSM begins to grow vertically (a process that can take one to five years), the chance of metastasis increases. Superficial spreading melanoma can affect any part of the body, and on average affects people between the ages of forty and fifty. The disease can occur at any age, however, and is the most common form diagnosed after puberty. The growth changes shape as the disease progresses, and usually presents as a dark growth, either flat or just slightly elevated. Superficial spreading melanoma may appear in a variety of colors.

Because it’s generally slow-growing, SSM has a good prognosis.

Nodular Melanoma (NM)

Types of Melanoma

Nodular melanoma is the second most common subtype after SSM, accounting for fifteen to twenty percent of cases. It has very little radial growth, but its vertical growth rate is aggressive. As a result, NM has a high rate of early metastasis. It may appear anywhere on the body, although sun-exposed areas are the most common locations.

Unlike other subtypes, nodular melanoma does not usually begin with a mole; instead, the tumor appears on normal skin. The tumor itself is small (usually less than one to two centimeters). It is often black or reddish-brown, and may be mistaken for a blood blister. The surface is elevated and round, and the borders are usually smooth. Nodular melanoma is usually diagnosed between the ages of forty and fifty, and is often well advanced at the time of diagnosis.

Due to its rapid growth rate and often widespread metastasis, NM has a very poor prognosis.

Acral Lentiginous Melanoma (ALM)

Acral lentiginous melanoma is the most common subtype for people with dark skin: sixty percent of melanomas diagnosed in darker-skinned people are ALM. The rate is much lower for light-skinned people, accounting for two to eight percent of all cases.

Acral lentiginous melanoma has a radial growth pattern, and is most often found on the palms, soles and under the fingernails. It can also be found in the mucous membranes. The growths may be quite large, often with diameters of over three centimeters.

An ALM lesion may look like a brown or black “blotch, ” a blood blister or a bruise that doesn’t heal. The disease spreads slowly radially across the skin, and then begins to grow vertically. The average age at diagnosis is sixty. Like NM, acral lentiginous melanoma is often well advanced at diagnosis.

The prognosis for ALM lies somewhere between SMM and NM. When ALM occurs in the mucous membranes the prognosis is unfavorable.

Lentigo Maligna Melanoma (LMM)

Lentigo maligna melanoma is the least common of the different types of melanoma, comprising only four to ten percent of all cases. It most often occurs on areas exposed to the sun. The tumor spreads radially, rarely growing into the skin, and is usually flat. The borders of the mole are often irregular, and it may grow as large as three to six centimeters. Lentigo maligna melanoma usually presents after the age of seventy, and is the least aggressive form of melanoma. The disease rarely metastasizes. While LMM generally has an excellent prognosis, lesions that are ignored or left untreated can eventually develop an unfavorable prognosis.

Ocular Melanoma

Cancerous melanocytes can also affect the eye, a condition known as ocular melanoma. The cancer may spread to the eye from a different location, but ocular melanoma can also be a primary tumor, originating on the eyelid, or in the pigment layers of the eye. Symptoms may not be apparent, although people may experience painful red eyes, bulging eyes, changes in eye color, and vision problems in the affected eye.

Ocular melanoma is treated with laser surgery, chemotherapy and radiation therapy. Without treatment, vision can be permanently affected, and the cancer may spread to the brain. If metastasis is a possibility, the eye may have to be removed to prevent the cancer from spreading to other organs.


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