Malignant melanoma is a type of skin cancer that develops in melanocytes, the cells responsible for producing the pigment that gives your skin its color. It accounts for a small percentage of all skin cancers but causes the majority of skin cancer deaths because of its ability to spread to other organs. Globally, about 332,000 new cases are diagnosed each year, with roughly 58,700 deaths.
How Melanoma Starts
Melanocytes sit in the outer layer of your skin and produce melanin, the pigment that darkens your skin in response to sunlight. When DNA in these cells becomes damaged, typically by ultraviolet (UV) radiation, they can begin to grow uncontrollably. Research from cell biology studies has shown that melanoma can originate specifically from melanocyte stem cells. These stem cells normally sit quietly in hair follicles and skin tissue, but UV exposure triggers an inflammation-driven process that activates them and causes them to migrate into surrounding skin, where they can form tumors.
This is why melanoma often appears as a new or changing spot on the skin, though it can also develop within an existing mole. Unlike many cancers that stay put for long periods, certain forms of melanoma become invasive quickly, growing downward through layers of skin and eventually reaching blood vessels or lymph nodes that carry cancer cells to distant organs.
The Four Main Types
Not all melanomas look or behave the same way. There are four primary subtypes, each with a distinct pattern of growth.
Superficial spreading melanoma is the most common type, making up about 70% of all cases. It grows outward across the skin surface for months or even years before it pushes deeper. These melanomas appear as flat or slightly raised brown patches with irregular borders and mixed coloring (black, blue, pink, or tan). In men, they tend to appear on the head, neck, and trunk. In women, the lower legs are a common site.
Nodular melanoma accounts for about 15% of cases and is more dangerous because it skips the slow horizontal growth phase and invades deeper tissue almost immediately. It typically looks like a raised, dome-shaped bump that is dark brown to black, though about 5% have no visible pigment at all, making them harder to spot.
Acral-lentiginous melanoma represents about 8% of all melanomas but is the most common type in people with darker skin, accounting for up to 70% of melanomas in Black individuals and 46% in Asian populations. It appears on the palms, soles of the feet, or under fingernails and toenails. Like nodular melanoma, it tends to progress aggressively.
Lentigo maligna melanoma makes up roughly 5% of cases and develops slowly on sun-exposed skin, usually in older adults. It can exist as a large, flat discoloration for many years before becoming invasive. When it does turn invasive, a darker raised nodule typically develops within the lesion.
Risk Factors
UV exposure is the single biggest environmental risk factor. Sunlight is the primary source, but tanning beds and sun lamps also contribute. Frequent sunburns, especially during childhood, are strongly linked to melanoma on the chest, back, and legs later in life.
Your physical traits also play a role. People with lighter skin face a much higher risk than those with darker skin. Within that group, those with red or blond hair, blue or green eyes, or skin that freckles or burns easily are at even greater risk. This partly explains why Europe and North America together account for about 78% of all melanoma cases worldwide.
Moles matter too. Having many moles increases your risk, and atypical moles (larger than normal, with irregular shape or color) raise it further. People with a hereditary condition called familial atypical multiple mole and melanoma syndrome, which involves numerous atypical moles plus a close relative with melanoma, face a very high lifetime risk. About 1 in 10 people diagnosed with melanoma have a family history of the disease.
A weakened immune system, whether from organ transplant medications, HIV, or other conditions, also increases susceptibility. And a rare inherited condition called xeroderma pigmentosum, which impairs the skin’s ability to repair UV-damaged DNA, carries particularly high risk even at a young age.
How to Spot It: The ABCDE Rule
The National Cancer Institute uses five visual features to help identify early melanoma:
- 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 mole has uneven shading with mixtures of black, brown, tan, white, gray, red, pink, or blue.
- Diameter: The spot is larger than about 6 millimeters (roughly the size of a pencil eraser), though melanomas can sometimes be smaller.
- Evolving: The mole has visibly changed in size, shape, or color over recent weeks or months.
Any single one of these features is worth getting checked. A spot that is evolving is particularly important to act on, even if it doesn’t meet the other criteria.
How Melanoma Is Diagnosed
If a spot looks suspicious, a dermatologist will remove some or all of it for examination under a microscope. There are a few ways this is done. A shave biopsy takes a thin slice from the top layers of skin and usually doesn’t require stitches. A punch biopsy uses a small circular cutting tool to remove a deeper sample. An excisional biopsy cuts out the entire suspicious area along with a margin of healthy skin and typically requires stitches. For a suspected melanoma, doctors generally prefer to remove the full lesion when possible so a pathologist can measure the tumor’s exact thickness.
That thickness, measured in millimeters, is the single most important factor in determining how serious the melanoma is. This measurement is called the Breslow depth. Current staging uses four main categories: 1 mm or less, 1.01 to 2 mm, 2.01 to 4 mm, and greater than 4 mm. The thicker the tumor has grown into the skin, the higher the stage and the greater the chance it has spread.
Stages and Survival Rates
Melanoma staging groups cases into three broad categories based on how far the cancer has spread. Localized melanoma, where the cancer is still confined to the original skin site, has a five-year survival rate above 99%. The vast majority of melanomas are caught at this stage. Regional melanoma, meaning it has spread to nearby lymph nodes or skin, has a five-year survival rate of 76%. Distant melanoma, where cancer has reached organs like the lungs, liver, or brain, has a five-year survival rate of 35%. Across all stages combined, the overall five-year survival rate is 95%.
These numbers are based on data from people diagnosed between 2015 and 2021, and outcomes for advanced melanoma have been improving thanks to newer treatments.
Treatment
For early-stage melanoma, surgery to remove the tumor and a surrounding margin of healthy skin is often the only treatment needed. The margin size depends on how thick the melanoma is. If there’s concern about spread, a procedure called sentinel lymph node biopsy checks whether cancer cells have reached the nearest lymph nodes.
For melanoma that has spread or can’t be fully removed with surgery, treatment has changed dramatically over the past decade. Two main approaches now form the backbone of advanced melanoma care.
Immunotherapy works by helping your immune system recognize and attack cancer cells. The most widely used drugs are checkpoint inhibitors, which block proteins that cancer cells use to hide from immune detection. These treatments can produce durable responses, meaning the cancer stays controlled for years in some patients. Different checkpoint inhibitors can also be combined for a stronger effect, though combination therapy tends to carry more side effects like fatigue, skin rashes, and inflammation in various organs.
Targeted therapy is an option when a melanoma carries specific genetic mutations. About 40 to 50% of melanomas have a mutation in a gene called BRAF, which drives cancer cell growth. Drugs that block the defective BRAF protein, often paired with a second drug that blocks a related growth signal, can shrink tumors rapidly. These combinations work best as a team, because using a BRAF-blocking drug alone often leads to the cancer finding a workaround within months.
Other treatments play more specialized roles. A form of cell therapy uses immune cells extracted directly from a patient’s tumor, grown in large numbers in a lab, and then infused back into the patient. An injectable virus-based therapy can be used for melanoma in the skin or lymph nodes that surgery can’t fully address. For very early or superficial lesions, a prescription immune-stimulating cream applied to the skin is sometimes an option.
Why Early Detection Changes Everything
The gap between a 99% survival rate for localized disease and 35% for distant disease makes melanoma one of the cancers where early detection matters most. A thin melanoma caught at under 1 mm is a routine outpatient procedure. A thick melanoma that has reached internal organs requires months of systemic treatment with real side effects and uncertain outcomes. Regular skin checks, both self-exams and periodic visits to a dermatologist if you have risk factors, remain the most effective way to catch melanoma when it is still highly curable.