Melanoma is a cancer that starts in the pigment-producing cells of your skin and, if not caught early, invades deeper tissue and spreads to organs throughout the body. Unlike many skin cancers that stay local, melanoma is aggressive. It can travel through the lymphatic system and bloodstream to the lungs, liver, brain, and bones, disrupting the function of each organ it reaches. What makes it particularly dangerous is how quickly it can progress from a small surface-level spot to a life-threatening disease.
How Melanoma Starts
Your skin contains cells called melanocytes, which produce the pigment that gives skin its color. When ultraviolet radiation from sunlight or tanning beds hits these cells, it damages their DNA directly. UVB rays cause bond distortions in the DNA strand, creating characteristic mutations where one DNA letter is swapped for another. About 80% of the immediate DNA damage takes the form of structural lesions that, if not repaired by the cell’s built-in repair machinery, become permanent mutations. UVA rays cause a different kind of damage by generating reactive oxygen species that attack DNA indirectly.
These mutations accumulate over a lifetime. Eventually, they can hit critical genes that control cell growth, cell death, and immune evasion. About 45% of melanomas carry a mutation in a gene called BRAF, which locks a growth-signaling pathway into the “on” position, telling the cell to keep dividing without stopping. Other mutations disable the genes that would normally force a damaged cell to self-destruct or allow the immune system to flag it for destruction. The result is a cell that grows uncontrollably, resists death, and hides from immune detection.
Not All Melanomas Come From Sun Damage
One subtype, called acral melanoma, develops on the palms of the hands, soles of the feet, and under fingernails or toenails, areas that get very little sun exposure. It accounts for a higher proportion of melanoma cases in people with darker skin. Non-nail acral melanomas appear on the foot in 82 to 89% of cases, and some researchers believe mechanical stress or trauma to these areas may play a role in triggering the disease. These melanomas have a different genetic profile, with fewer overall mutations but more structural rearrangements in the DNA. They also tend to have a more suppressive immune environment around them, which can make them harder to treat.
What Melanoma Looks Like on the Skin
The ABCDE criteria are the standard way to evaluate a suspicious mole or spot:
- Asymmetry: one half doesn’t match the other
- Border: edges are uneven, ragged, or blurred
- Color: multiple shades or colors within the same spot (brown, black, red, white, or blue)
- Diameter: larger than a pencil eraser (about 6 mm), though melanomas can be smaller
- Evolving: any change in size, shape, color, or height, or new symptoms like itching, bleeding, or scabbing
The “E” is often the most important. A mole that is changing in any way warrants attention, even if it doesn’t meet all the other criteria.
How It Invades and Spreads
Melanoma’s danger lies in its ability to grow downward into the skin and then travel to distant parts of the body. Doctors measure how deep a melanoma has penetrated using a measurement called Breslow thickness, recorded in tenths of a millimeter from the surface of the skin (or the base of an ulcer) to the deepest tumor cells. A melanoma that is 0.4 mm thick is a very different disease from one that is 4.0 mm thick. Thicker tumors are linked to significantly lower survival rates.
Once melanoma reaches the lymphatic system or bloodstream, it can seed new tumors almost anywhere. The most common sites it spreads to are, in order: the skin and tissue just beneath it (subcutaneous nodules can be the first sign of spread), followed by the lungs, liver, bones, and brain. Melanoma has a particularly strong tendency to reach the central nervous system, partly because it can cross the blood-brain barrier, which also makes brain metastases harder to treat.
What It Does to Organs
The damage melanoma causes depends on where it lands. Each organ responds differently, and the symptoms reflect the disruption to that organ’s normal function.
Lungs
Lung metastases are the most common cause of death from metastatic melanoma. They cause respiratory failure as tumor growth replaces functional lung tissue. Symptoms include a persistent cough, shortness of breath, coughing up blood, and fluid buildup between the chest wall and lung.
Brain
Brain involvement is the second most common cause of melanoma-related death. Bleeding occurs in most patients with brain metastases from melanoma, which can cause sudden, severe headaches. Other symptoms include memory problems, personality or mood changes, seizures, confusion, and weakness in an arm or leg.
Liver
The liver is the most common internal organ affected by melanoma spread. As tumors grow within the liver, they impair its ability to filter blood and produce essential proteins. This can cause pain or discomfort on the right side of the abdomen, nausea, weight loss, a swollen abdomen from fluid accumulation, yellowing of the skin, and itching.
How Stage Affects Survival
Melanoma survival rates vary dramatically depending on when it’s found. Data from the National Cancer Institute’s SEER program, covering cases from 2016 to 2022, shows a stark picture:
- Localized (confined to the original site): 100% five-year survival
- Regional (spread to nearby lymph nodes): 76% five-year survival
- Distant (spread to remote organs): 34% five-year survival
That 100% figure for localized melanoma is remarkable and underscores why depth of invasion matters so much. A thin melanoma caught before it spreads is almost universally survivable. Once it reaches distant organs, the odds shift substantially, though the 34% distant survival rate has improved significantly in recent years thanks to newer treatments.
How Treatment Works Against Melanoma
Two major treatment advances have reshaped outcomes for advanced melanoma. The first targets the BRAF mutation directly. Because nearly half of melanomas depend on this mutated protein to fuel their growth, drugs that block the mutant BRAF protein can shut down the signaling pathway driving cell division.
The second, and arguably more transformative, approach is immunotherapy. Melanoma cells protect themselves by displaying proteins on their surface that essentially tell immune cells to stand down. Checkpoint inhibitor drugs work by blocking this interaction. One type prevents melanoma cells from deactivating the T cells that would otherwise attack them. Another type releases a separate brake on T cells, boosting their ability to multiply and produce the chemical signals needed to mount a full immune response. The net effect is that the immune system “sees” the melanoma again and attacks it. These therapies have turned some cases of metastatic melanoma, once considered rapidly fatal, into long-term survivable disease.