Cutaneous melanoma is a skin cancer that develops when pigment-producing cells called melanocytes turn malignant. These cells sit in the deepest layer of your epidermis (the outermost sheet of skin), where they normally produce melanin to give skin its color. When UV radiation or genetic factors cause irreparable DNA damage in these cells, they can begin growing out of control. It is the most dangerous form of skin cancer, but the five-year survival rate for melanoma caught before it spreads is effectively 100%.
How Melanocytes Become Cancerous
Melanocytes are scattered along the base of your epidermis. Ultraviolet radiation, primarily from the sun, damages their DNA in two ways. It creates direct oxidative stress that disrupts the cells, and it interferes with the body’s normal DNA repair machinery. When enough of these errors accumulate and the cell can no longer fix itself, mutations begin driving uncontrolled growth. The result is a melanoma that initially spreads horizontally across the skin surface and may eventually grow downward into deeper tissue, where it gains access to blood vessels and lymph nodes.
About 38.5% of cutaneous melanomas carry a mutation in a gene called BRAF, which acts like a stuck accelerator for cell growth. Another 16.4% have mutations in NRAS, a related growth-signaling gene. These molecular details matter because they determine which targeted therapies may work if treatment beyond surgery is needed.
The Four Main Subtypes
Cutaneous melanoma isn’t one disease. It appears in four distinct forms, each with different growth patterns and locations.
Superficial spreading melanoma is the most common type. It grows horizontally across the skin for years before pushing deeper. It looks like a flat or slightly raised brown patch with irregular, asymmetric borders and may contain black, blue, or pink areas. These lesions are typically larger than 6 mm across.
Nodular melanoma is the most aggressive subtype. Unlike superficial spreading melanoma, it invades deeper tissue almost immediately. It usually appears as a dome-shaped bump that is dark brown to black, though about 5% have no pigment at all, making them harder to spot.
Lentigo maligna melanoma tends to develop on sun-damaged skin in older adults. It can exist as a flat, slowly expanding patch for many years before becoming invasive. The precursor lesion is often larger than 3 cm in diameter, and invasion is signaled by the appearance of a raised, dark nodule within the patch.
Acral-lentiginous melanoma occurs on the palms, soles, and under fingernails or toenails. It is the most common subtype in people with darker skin tones. Like nodular melanoma, it progresses rapidly from surface-level growth to deep invasion.
Who Is at Highest Risk
Ultraviolet radiation is the primary risk factor, and because it is behavioral, melanoma is considered largely preventable. Both natural sunlight and artificial sources like tanning beds deliver UV radiation that the International Agency for Research on Cancer has classified as carcinogenic across its full spectrum.
Lighter skin increases risk substantially. People with Fitzpatrick skin type III (burns moderately, tans gradually) have roughly 1.8 times the melanoma risk of those with type IV skin (burns minimally, tans easily). Having many moles, a history of severe sunburns, or a family history of melanoma also raises the odds.
Genetics play a role beyond skin color. Variants in the MC1R gene, which shifts pigment production toward the type associated with red hair and freckles, increase melanoma odds by about 1.4 times for one variant and 2.5 times for two or more variants. Interestingly, this genetic risk is most pronounced in people who don’t have the typical red-hair phenotype, meaning darker-skinned individuals with these hidden gene variants still face elevated risk. Mutations in tumor suppressor genes like BAP1, BRCA1, BRCA2, and others linked to mixed cancer syndromes also raise melanoma susceptibility.
Spotting Melanoma Early: The ABCDE Criteria
The ABCDE framework gives you a practical checklist for evaluating any mole or pigmented spot on your skin:
- Asymmetry: One half of the mole doesn’t match the other.
- Border: The edges are ragged, notched, or blurred, and pigment may spread into surrounding skin.
- Color: The color is uneven, with shades of black, brown, tan, or patches of white, gray, red, pink, or blue.
- Diameter: The spot is larger than 6 mm (about the size of a pencil eraser), though melanomas can start smaller.
- Evolving: The mole has changed in size, shape, or color over weeks or months.
Any single one of these features warrants a closer look. A combination of two or more is a strong reason to get a professional evaluation promptly.
How Melanoma Is Staged
Once a biopsy confirms melanoma, staging tells you how far it has progressed. The most important measurement is Breslow depth: how many millimeters the tumor extends below the skin surface.
Thin melanomas (1 mm or less) without ulceration are classified as Stage IA. Melanomas between 1.01 and 2 mm fall into Stage IB or IIA depending on whether the surface is ulcerated (broken). Tumors between 2.01 and 4 mm are Stage IIB, and anything thicker than 4 mm is Stage IIC. Once melanoma reaches nearby lymph nodes, it becomes Stage III. Spread to distant organs is Stage IV.
If a melanoma is thicker than 0.8 mm, or thinner than 0.8 mm but ulcerated, guidelines recommend a sentinel lymph node biopsy. This procedure checks whether cancer cells have reached the closest lymph node, which is the single strongest predictor of whether the disease will spread further. Younger patients, those with rapidly dividing tumor cells, or those whose biopsy margins weren’t clear may also be offered this procedure even for very thin melanomas.
Survival by Stage
Melanoma caught early has an excellent prognosis. According to National Cancer Institute data from 2015 to 2021, the five-year relative survival rate for localized melanoma (confined to the original site) is 100%. When it has spread to regional lymph nodes, survival drops to 75.7%. For distant metastatic melanoma, the five-year survival rate is 34.6%, though newer immunotherapy treatments have been steadily improving that number.
These statistics underscore why thickness at diagnosis matters so much. A melanoma found at 0.5 mm is a fundamentally different disease from one found at 4 mm, even though both start from the same cell type.
Surgical Treatment and Margins
Surgery is the primary treatment for cutaneous melanoma, and the amount of surrounding skin removed depends directly on tumor thickness. For melanoma in situ (confined to the epidermis with no invasion), surgeons remove a margin of 5 mm to 1 cm of healthy skin around the visible lesion. For invasive melanomas, wider margins are required, scaled to Breslow depth.
Lentigo maligna melanoma on the head and neck poses a particular challenge. A standard 5 mm margin often leaves behind cancer cells in these cases because the lesion’s true edges can be hard to define visually. Specialized techniques that examine 100% of the margin tissue under a microscope during surgery help ensure complete removal in these tricky locations.
For thicker or higher-risk melanomas, surgery may be followed by immunotherapy or targeted therapy. Tumors with BRAF mutations can be treated with drugs that block that specific growth signal. Immunotherapy drugs that help the immune system recognize and attack melanoma cells have transformed outcomes for advanced disease over the past decade, particularly for patients whose cancer has spread to lymph nodes or distant sites.