Melanoma is a type of skin cancer that starts in melanocytes, the cells responsible for producing the pigment that gives your skin its color. These cells normally make a brown pigment called melanin, which protects deeper layers of skin from sun damage. When melanocytes begin growing out of control, the result is melanoma, the most serious form of skin cancer.
How Melanoma Develops
Your skin is constantly exposed to ultraviolet (UV) radiation from the sun. When UV rays hit melanocytes, they can damage the DNA inside those cells. Normally, cells repair this damage or self-destruct if the damage is too severe. But sometimes the mutations accumulate in genes that control cell growth and survival. The damaged melanocytes lose their built-in growth limits and begin multiplying without stopping.
About 50% of all melanomas carry a specific mutation in a gene called BRAF, which acts like a stuck accelerator pedal for cell growth. This discovery has been important for treatment, since doctors can now test tumors for this mutation and use drugs designed to target it directly.
UV exposure isn’t the only factor. Genetics, skin type, the number of moles you have, and family history all influence your risk. People with fair skin, light eyes, and a history of severe sunburns are at higher risk, but melanoma can develop in anyone.
The Four Main Types
Superficial spreading melanoma is by far the most common, accounting for roughly 70% of all cases. It grows outward across the skin surface for months or even years before pushing deeper. It typically appears as a flat or slightly raised brown spot with irregular borders and uneven color, often larger than 6 millimeters (about the size of a pencil eraser).
Nodular melanoma makes up about 15% of cases and is more aggressive. Rather than spreading across the surface first, it grows downward into the skin quickly. It often looks like a raised, dome-shaped bump that’s dark brown or black, though about 5% have no pigment at all and can resemble a blood blister or pimple.
Acral lentiginous melanoma represents about 8% of melanomas overall, but it’s the most common type in people with darker skin, accounting for up to 70% of melanomas in Black patients and 46% in Asian patients. It appears on the palms, soles of the feet, or under fingernails and toenails, areas that many people don’t think to check.
Lentigo maligna melanoma accounts for roughly 5% of cases and develops on sun-exposed skin, usually in older adults. It can exist as a flat, irregularly colored patch for many years before becoming invasive. By the time it does, the precursor spot is often larger than 3 centimeters.
How to Spot It: The ABCDE Rule
Dermatologists use a simple framework to identify suspicious moles and spots:
- Asymmetry: One half of the mole doesn’t match the other.
- Border: The edges are ragged, notched, or blurred rather than smooth.
- Color: The pigment is uneven, with shades of brown, black, tan, or even areas of white, red, pink, or blue.
- Diameter: The spot is larger than 6 millimeters, though melanomas can sometimes be smaller.
- Evolving: The mole has changed in size, shape, or color over recent weeks or months.
Any single one of these features is worth getting checked. A mole that’s evolving is particularly important, even if it doesn’t meet the other criteria yet.
How Thickness Determines Severity
Once melanoma is diagnosed, the single most important measurement is how deep it has grown into the skin, measured in millimeters. A pathologist examines the removed tissue under a microscope and reports this depth to the nearest tenth of a millimeter. Thinner melanomas have a dramatically better outlook than thicker ones.
Staging also depends on whether the cancer has spread beyond the original site. The five-year survival rates tell the story clearly: melanoma caught while still localized to the skin has a five-year survival rate of virtually 100%. Once it has reached nearby lymph nodes, that drops to 76%. If it has spread to distant organs like the lungs, liver, or brain, the five-year survival rate falls to 34%. This is why early detection matters so much.
Treatment Options
Surgery is the primary treatment for melanoma that hasn’t spread. The surgeon removes the melanoma along with a margin of healthy skin around it. How wide that margin needs to be depends on the tumor’s thickness: melanoma that hasn’t grown beyond the skin’s surface layer requires only a 0.5 to 1 centimeter margin, while thicker tumors need up to 2 centimeters of surrounding tissue removed. For many early-stage patients, surgery is the only treatment needed.
For melanoma that has spread or is at high risk of returning, treatment has changed dramatically in the past decade. Immunotherapy drugs work by removing the “off switch” that cancer cells use to hide from the immune system. Normally, cancer cells display proteins on their surface that tell immune cells to stand down. These drugs block that signal, allowing the body’s own immune cells to recognize and attack the cancer. Several classes of these drugs now exist, targeting different checkpoint proteins on immune cells.
For the roughly half of melanomas carrying BRAF mutations, targeted therapy drugs can shut down the specific growth signal driving the cancer. These treatments often produce rapid responses, sometimes shrinking tumors within weeks. They’re frequently combined with immunotherapy for advanced disease.
Why Melanoma Is Different From Other Skin Cancers
The two most common skin cancers, basal cell and squamous cell carcinoma, arise from different cell types and rarely spread to distant parts of the body. Melanoma is less common but far more dangerous because melanocytes have a natural ability to migrate. During embryonic development, melanocytes travel from one tissue layer to populate the skin, hair follicles, and even the eyes. When these cells become cancerous, they retain that tendency to move, which is why melanoma can metastasize to virtually any organ.
Melanoma can also develop in places other than the skin. Because melanocytes exist in the eyes, mouth, and digestive tract, melanoma occasionally arises in these locations. These cases are rarer and not related to sun exposure, reinforcing that UV damage is a major but not exclusive cause.