Melanoma is a skin cancer that starts in melanocytes, the cells that give your skin its color. It’s less common than other skin cancers but far more dangerous because it can spread to other parts of the body quickly. When caught early and still confined to the skin, the five-year survival rate is effectively 100%. Once it spreads to distant organs, that number drops to 34%.
How Melanoma Develops
Melanocytes sit in the deepest layer of your outer skin, attached to neighboring cells through molecular anchors that keep them in check. Those neighboring cells regulate how melanocytes grow and behave. When DNA damage accumulates, typically from ultraviolet radiation, melanocytes can break free from that control. They swap the molecular anchors that kept them tethered for different ones that let them migrate deeper into the skin and interact with blood vessels.
This is what makes melanoma uniquely aggressive compared to other skin cancers. Basal cell and squamous cell carcinomas grow slowly and rarely spread beyond the original site. Melanoma cells actively acquire the ability to travel, which is why a small spot on your skin can seed cancer in your lungs, liver, or brain if it isn’t caught in time.
The ABCDE Rule for Spotting Melanoma
The National Cancer Institute uses a five-feature checklist to help people recognize melanoma early. You don’t need all five features to be concerned. Any one of them is worth getting checked.
- Asymmetry: One half of the mole doesn’t match the other. Normal moles are roughly symmetrical.
- Border irregularity: The edges are ragged, notched, or blurred rather than smooth. Pigment may spread into the surrounding skin.
- Color variation: Instead of one uniform shade, you see a mix of brown, tan, black, or unexpected colors like white, gray, red, pink, or blue within the same spot.
- Diameter: Most melanomas are larger than 6 millimeters across, roughly the size of a pencil eraser, though they can be smaller.
- Evolving: The mole has changed in size, shape, or color over weeks or months. This is often the single most important warning sign.
The Four Main Types
Superficial Spreading Melanoma
This is the most common type. It appears as a flat or slightly raised brown spot with patches of black, blue, or pink. It’s typically wider than 6 millimeters with irregular, asymmetric borders. It grows outward across the skin surface before growing deeper, which usually gives you more time to notice it.
Nodular Melanoma
This type doesn’t play by the ABCDE rules. Instead of spreading outward as a flat spot, it grows as a firm, dome-shaped bump, often dark brown to black, that can look like a blood blister. It develops fast, sometimes over just a few weeks. Because it grows downward into the skin rather than outward, it can reach dangerous depths before it looks very large on the surface. If you notice a new raised bump that is firm, elevated, and growing steadily, that combination alone warrants attention.
Lentigo Maligna Melanoma
This type appears on sun-damaged skin, usually on the face, ears, or arms of older adults. It starts as a flat, tan or brown patch that slowly darkens over years. When it becomes invasive, it develops dark brown-to-black coloring or a raised blue-black nodule within the flat patch.
Acral Lentiginous Melanoma
This is the type most often missed, and it deserves special attention. It shows up on the palms of your hands, soles of your feet, or under your fingernails and toenails. These are spots most people never think to check for skin cancer, and because they aren’t sun-exposed areas, many people assume they’re safe. They’re not.
Acral lentiginous melanoma is the most common form of melanoma in people of Latin American, African, and Asian descent. It’s frequently misdiagnosed as a fungal infection, a wart, or a foot ulcer, which delays treatment and leads to later-stage diagnoses. Under a nail, it often appears as a dark streak running the length of the nail (longitudinal melanonychia). Signs that point toward melanoma rather than a harmless streak include irregular coloring within the band, a width covering more than two thirds of the nail, black or grey pigment, and pigment that bleeds into the skin around the nail (called Hutchinson’s sign).
The standard ABCDE checklist is less reliable for these lesions because they look different from typical moles. An alternative screening tool called CUBED was developed specifically for feet and nails: Colored lesion, Uncertain diagnosis, Bleeding on the foot or under the nail, Enlargement, and Delay in healing beyond two months.
What Happens After You Find Something
A dermatologist will examine the spot visually, often with a handheld magnifying device called a dermatoscope that reveals patterns invisible to the naked eye. If the spot looks suspicious, the next step is a biopsy, where all or part of the lesion is removed and examined under a microscope.
If the biopsy confirms melanoma, the single most important number in your pathology report is the depth measurement, recorded in fractions of a millimeter. A melanoma less than 1 millimeter deep has an excellent prognosis and usually requires only surgical removal with a margin of normal skin around it. As the depth increases, so does the likelihood that cancer cells have reached lymph nodes or blood vessels. Melanomas deeper than 4 millimeters carry significantly higher risk of spread and typically require additional testing to check for metastasis.
Why Early Detection Changes Everything
The survival gap between early and late detection is enormous. SEER data covering 2016 through 2022 shows that localized melanoma, meaning cancer that hasn’t spread beyond the original site, has a five-year survival rate of 100%. When it has spread to nearby lymph nodes, that drops to 76%. When it has reached distant organs, it falls to 34%. Immunotherapy and targeted treatments have improved outcomes for advanced melanoma dramatically over the past decade, but the math still overwhelmingly favors catching it early.
The practical takeaway is straightforward: check your skin regularly, including the spots you’d never expect, like between your toes, on your soles, and under your nails. Pay attention to any mole or mark that is changing. A monthly self-check in good lighting takes five minutes and gives you the best chance of catching melanoma when it’s still completely curable.