Melanoma is a cancer that starts in melanocytes, the pigment-producing cells in the outer layer of your skin. It accounts for a small fraction of all skin cancers but causes the majority of skin cancer deaths because of its ability to spread to other organs. Caught early and still confined to the skin, the five-year survival rate is effectively 100%. Once it reaches distant organs, that number drops to 34%.
How Melanoma Develops
Melanocytes sit in the deepest layer of the epidermis, where they produce melanin, the pigment that gives skin its color. When DNA in these cells is damaged, typically by ultraviolet radiation, mutations can disable the normal controls on cell growth and division. About 75% of melanomas involve mutations in two specific growth-signaling pathways that essentially lock the cell into a state of constant proliferation. Roughly half of all melanomas carry a mutation called BRAF V600E, which has become a major target for treatment.
What makes melanoma particularly dangerous is its tendency to shift from horizontal growth (spreading outward across the skin surface) to vertical growth (pushing deeper into the skin and toward blood vessels and lymph nodes). Once melanoma cells reach the bloodstream or lymphatic system, they can travel to the lungs, liver, brain, or bones.
The Four Main Types
Not all melanomas look or behave the same way. They fall into four primary subtypes.
Superficial spreading melanoma is the most common form, especially in fair-skinned people. It grows slowly outward as a flat, irregular lesion with brown or black coloring. In women, it tends to appear on the lower legs; in men, on the back.
Nodular melanoma is more aggressive. Instead of spreading across the surface first, it grows downward into the skin relatively quickly. It typically appears as a raised, dark, dome-shaped bump, sometimes on the head, neck, or back in men and the legs in women. Patients often notice bleeding, itching, or stinging at the site.
Lentigo maligna melanoma shows up most often on the head and neck of older adults with significant sun damage. It starts as a large, slowly growing flat patch with uneven pigmentation and irregular borders.
Acral lentiginous melanoma develops on the palms, soles, fingers, toes, and under the nails. It can look like a wound, wart, or bruise, which means it’s frequently misdiagnosed or caught late. This is the most common form of melanoma in people with darker skin tones, and it has nothing to do with sun exposure.
Risk Factors
UV radiation is the dominant environmental risk factor. Childhood sunburns are especially significant: some research suggests they can double melanoma risk later in life. The total number of sunburns over a lifetime also matters, not just those in childhood. Indoor tanning before age 30 increases melanoma risk by 75%.
Your skin’s pigment chemistry plays a role beyond just being “fair” or “dark.” People with red hair and freckles carry a variant in the gene that controls melanin production, causing their skin to produce a form of pigment called pheomelanin instead of the more protective eumelanin. Pheomelanin doesn’t just fail to protect against UV damage; it actively generates free radicals that can harm DNA when exposed to UV light. Interestingly, some of these pigment gene variants increase melanoma risk regardless of hair color or skin type.
Family history accounts for 3% to 15% of melanomas. If you have a first-degree relative who has had melanoma, your risk is meaningfully elevated. Having a large number of moles, particularly unusual-looking ones (more than five atypical moles, or more than 100 ordinary moles), also raises risk substantially.
How to Spot It: The ABCDE Rule
The National Cancer Institute uses five visual features to describe early melanoma:
- Asymmetry: one half of the mole doesn’t match the other
- Border: edges are ragged, notched, or blurred, sometimes with pigment spreading into surrounding skin
- Color: uneven shading with mixtures of black, brown, tan, white, gray, red, pink, or blue
- Diameter: most melanomas are larger than 6 millimeters (about the size of a pencil eraser), though they can be smaller
- Evolving: any change in size, shape, or color over weeks or months
The “evolving” criterion is often the most useful in practice. A mole that has looked the same for years is far less concerning than one that’s changing. Any new mole that looks different from your other moles also warrants attention.
Melanoma vs. Other Skin Cancers
About 80% of skin cancers are basal cell carcinomas, and another 20% are squamous cell carcinomas. Melanoma is far less common than either, but it behaves very differently. Basal cell carcinoma grows slowly and almost never spreads beyond the skin. Squamous cell carcinoma is more likely to invade deeper tissue but still spreads relatively rarely. Melanoma, by contrast, can metastasize early and aggressively if not caught in time. This is why a melanoma diagnosis carries urgency that other skin cancers typically don’t.
How Thickness Determines Stage
When a suspicious lesion is biopsied, the single most important measurement is its thickness, measured in millimeters from the skin surface to the deepest point of tumor invasion. This is called Breslow depth, and it drives staging and treatment decisions.
Melanomas 1 millimeter or thinner are classified as Stage I. Between 1 and 2 millimeters falls into Stage I or II depending on whether the surface is ulcerated. Tumors between 2 and 4 millimeters thick are Stage II, and anything thicker than 4 millimeters is advanced Stage II. Once melanoma has spread to nearby lymph nodes, it’s Stage III. Spread to distant organs is Stage IV. Whether the tumor’s surface is broken (ulcerated) bumps the staging up at every thickness level, because ulceration signals more aggressive behavior.
Treatment
For early-stage melanoma still confined to the skin, surgery to remove the tumor with a margin of healthy tissue around it is typically curative. The width of that margin depends on thickness: thinner melanomas need smaller margins.
For melanoma that has spread to lymph nodes or beyond, treatment has changed dramatically in the past decade. About half of all melanomas carry the BRAF mutation, and targeted drugs that block this mutation’s signaling pathway can shrink tumors significantly. These are taken as pills and work by cutting off the specific growth signal the cancer depends on.
Immunotherapy has become the other major pillar of advanced melanoma treatment. These drugs work by releasing the brakes on your immune system so it can recognize and attack melanoma cells. For metastatic melanoma, immunotherapy has extended survival in ways that were not possible before 2010. Combining immunotherapy drugs that target different immune checkpoints tends to produce stronger responses than using either alone, though it also increases side effects.
Survival Rates by Stage
Data from the National Cancer Institute’s SEER program, covering cases diagnosed between 2016 and 2022, shows stark differences by stage at diagnosis. Localized melanoma, still confined to the original site, has a five-year relative survival rate of 100%. Regional melanoma, meaning it has reached nearby lymph nodes, drops to 76%. Distant melanoma, which has spread to other organs, has a 34% five-year survival rate. That distant-stage number has improved considerably in recent years thanks to immunotherapy and targeted drugs, but it underscores why early detection matters so much.
Screening and Self-Exams
The American Cancer Society recommends periodic skin checks as part of routine health exams for adults over 20, and advises monthly self-exams for anyone with a family history of melanoma. The American Academy of Dermatology encourages regular self-exams for everyone, even without a personal history of skin cancer. For people at high risk, such as those with a history of melanoma or multiple atypical moles, guidelines from several countries recommend professional skin exams every six months and self-checks every three months.
A useful self-exam technique is to stand in front of a full-length mirror and systematically check your entire body, using a hand mirror for your back, scalp, and the soles of your feet. Pay attention to any mole that looks different from the rest, sometimes called the “ugly duckling” sign. Photograph moles you want to track so you can compare over time.