What it is: The most common type of melanoma, representing about 70% of all cases. This melanoma usually appears as a flat or barely raised lesion, often with irregular borders and variations in color. These melanoma lesions most commonly appear on the trunks of men, the legs of women, and the upper back of both sexes. These lesions are diagnosed most frequently in patients between the ages of 30 and 50. About half of these melanomas occur in pre-existing moles.1
How it progresses: Even though it may spread, it spreads along the top layer of skin, the epidermis, for a period of months to years before it goes deeper into the skin.
Signs: The darkening in one part of a pre-existing mole or the appearance of a new mole on unaffected, normal skin.
What it is: A melanoma that is found most often on the trunk, the head, or the neck, and represents 10% to 15% of all melanomas. Nodular melanoma is more common in men than women.
How it progresses: Unlike other melanomas that tend to grow across the surface of the skin (like an oil slick spreading), a nodular melanoma invades deeply earlier and therefore often presents with a greater depth of invasion when it is found and biopsied. For this reason, nodular melanomas are more frequently associated with a poorer prognosis than other melanomas.
Signs: This melanoma usually appears as a blue-black, dome-shaped nodule, although 5% of the time the lesions are pink or red.
What it is: This melanoma comes from a preexisting lentigo, rather than a mole. Historically, only about 5% of all melanoma cases are lentigo maligna melanoma
How it progresses: This type of melanoma typically takes many years to develop. It occurs most often in older adults, usually on the face and other chronically sun-exposed areas. Unlike nodular melanoma which has had a fairly stable rate of occurrence, the rate of lentigo maligna melanoma has been steadily increasing over the last decades. This increase is thought to be due to the fact that the development of lentigo maligna melanoma is more influenced by chronic sun exposure.2
Signs: These melanomas are generally large, flat, tan-colored lesions containing differing shades of brown, or as in other melanomas, black, blue, red, gray, or white.
What it is: “Acral” comes from the Greek word akron, meaning extremity, and the disease typically appears on the palms, soles, or under the nails. Less than 5% of all melanomas are acral lentiginous melanoma (subungual melanoma), but it is the most common melanoma in African-Americans and Asians.
How it progresses: Because of the misconceptions that melanomas only occur in sun-exposed areas and that dark-skinned and Asian people are not at risk for melanoma, these melanomas are often discovered later than other forms.
Signs: These melanomas look like bruises or injuries to the palms, soles, or nail beds, which is why they are often not diagnosed early. When they appear as lesions, they are usually tan, brown, or black, with variations in color and irregular borders. When a melanoma occurs under the fingernail or toenail, it may present as a brown, black, or even a blue streak in the nail. In darkly pigmented individuals such as African Americans, it can be completely normal to have darker streaks under the nail because of the increased amount of melanin that their normal melanocytes produce. However, in a Caucasian or similarly lightly pigmented person, dark streaks in the nail are very rare, and any streak that cannot be explained by a trauma must be seriously considered for a biopsy to prove that there is no cancer under the nail.
Melanomas Without a Primary (Internal Areas)
About 5% to 10% of melanomas are found first in internal areas of the body, such as lymph nodes or internal organs without any obvious signs on the skin.
Some doctors believe most of these melanomas originate on the skin 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 skin 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 are transformed into melanoma
Ocular melanoma is melanoma that is found in the eye, and is relatively uncommon, accounting for only 3% of all melanoma cases. However, ocular melanoma is the most common type of primary intraocular cancer in adults. (Primary intraocular cancer means that the tumor started in the eye). It begins when pigmented (colored) cells in the eye called melanocytes grow uncontrollably. Intraocular melanoma is also called uveal melanoma because it occurs in the part of the eye called the uvea.
Ocular melanomas occur in five distinct sites around and in the eye. Each type has its own distinctive growth pattern and prognosis:
- Eyelid Melanoma – Essentially like other skin (cutaneous) melanomas
- Conjunctival Melanoma – The filmy white covering of the eye
- Iris Melanoma – The colored part of the inside of the eye around the pupil
- Choroidal Melanoma – The pigmented supporting layer under the retina containing large numbers of blood vessels
- Optic Nerve Melanoma – The large ‘nerve of vision’ which exits the back of the eye
What is NOT Melanoma
- Most common type of skin cancer in fair-skinned people
- Grows very slowly and very rarely will spread to other parts of the body
- Usually found on face, ears, scalp, neck, or upper body
- Can appear as: a red patch, a pink, red, or white bump that is shiny or pearly, an open sore that will not heal, a scar-like area
- Second most-common type of skin cancer in fair-skinned people
- Slow-growing but can spread to other parts of the body
- Twice as common in men as in women
- May appear as a bump or scaly red patch on the face, neck, arms, scalp, ears, lips, or mouth
- Squamous-cell carcinoma of the lips is strongly associated with smoking or use of chewing tobacco and spreads much more frequently than other cancer types
- Moles [medical term: nevus or nevi (plural)]: evenly-colored, even borders, tan or dark brown
- Congenital nevi: present at birth or within first year
- Atypical nevi: moles that are large or have an irregular shape or blurred border; may be pink, brown, or black
- Freckles: small, tan, flat spots caused by chronic or intense sun exposure. The presence of freckles is a marker for the amount of sun damage one has had.
- Lentigines: called sunspots, age spots, or liver spots; flat brown and do not fade like freckles when not in sun. People with lentigines have had a great deal of sun exposure and are at higher risk for skin cancers.
- Seborrheic keratosis: raised, rough, scaly lesions that are usually light brown to almost black in color. They are caused by an excessive growth of the upper layers of the skin. They do not turn into melanoma. They are usually found on the back, chest, arms, and face.
Where Melanomas Start
Most Melanomas Occur on the Skin
Source of Melanomas on the Skin
Age spots (liver spots) – usually occur in people 70 or older
How Melanoma Develops
Melanoma develops in a manner similar to other cancer types. A cell’s DNA genes, which control cell division and reproduction, become damaged. The damaged genes cause the cell to divide and grow without control or order, eventually becoming a malignant tumor.
In the case of melanoma, the damage to the DNA is usually caused by overexposure to ultraviolet (UV) radiation, and the affected cells are melanocytes, which produce the pigment melanin. The first tumor that develops is usually located in the skin. If not caught, melanoma will grow and spread along the epidermis before penetrating deeper layers of the skin and eventually coming into contact with lymph and blood vessels.
In this section, you’ll find details of how melanoma develops from normal cells into tumors and, if not checked, eventually spreads through the lymph vessels and bloodstream.
1. Skender-Kalnenas TM. J Am Acad Dermatol. 1995;33:1000-1007.
2. Forman SB. J Am Acad Dermatol. 2008;58(6):1013-1020.