Melanoma is the most dangerous form of skin cancer, but it accounts for only about 1 in 20 skin cancer diagnoses

Melanoma is a cancer that starts in melanocytes—the cells in your skin that produce the pigment melanin, which gives skin its color. Unlike basal cell carcinoma and squamous cell carcinoma, which grow slowly and rarely spread, melanoma can grow quickly and spread to other parts of your body if not caught early. This capacity to spread is what makes it more serious, even though it is less common than the other two types.

Melanoma can appear anywhere on your skin, though it most often develops on areas exposed to the sun. It can also grow in places the sun does not reach—under fingernails, on the soles of feet, or inside the eye. The appearance varies widely: some melanomas are dark brown or black, while others are tan, red, or even colorless. This variability is one reason why any changing or unusual skin growth should be examined by a doctor.

Key Takeaways

  • Melanoma starts in melanocytes and can spread to lymph nodes and distant organs, making it more dangerous than basal cell or squamous cell skin cancer.
  • The ABCDE rule—Asymmetry, Border irregularity, Color variation, Diameter larger than a pencil eraser, and Evolving (changing)—helps identify suspicious moles that warrant medical evaluation.
  • Melanoma is staged from 0 to IV based on thickness, whether it has spread to lymph nodes, and whether it has reached distant organs.
  • Early detection significantly improves outcomes; melanomas caught before they spread to lymph nodes have much higher survival rates than those that have spread.
  • Risk factors include fair skin, family history of melanoma, many moles, severe sunburns in childhood, and use of tanning beds.

How melanoma develops and spreads

Melanoma begins when melanocytes grow abnormally and form a tumor in the outer layer of skin called the epidermis. In its earliest stage, called melanoma in situ, the cancer cells remain only in the epidermis and have not invaded deeper layers. At this stage, the risk of spread is very low.

As melanoma progresses, it can grow downward into the dermis—the layer of skin beneath the epidermis. Once it reaches a certain depth, it gains access to blood vessels and lymphatic vessels, which are the pathways cancer cells use to travel to other parts of the body. Melanoma cells can lodge in nearby lymph nodes first, then spread to the lungs, liver, brain, or bones. This progression is why thickness—how deep the melanoma has grown into the skin—is one of the most important factors in determining prognosis.

The ABCDE warning signs

Doctors and dermatologists use the ABCDE rule as a simple way to identify moles that may be melanoma and need professional evaluation:

  • Asymmetry: One half of the mole does not match the other half.
  • Border: The edge is irregular, scalloped, or poorly defined rather than smooth and even.
  • Color: The mole contains multiple colors—brown, black, tan, red, white, or blue—rather than a single uniform shade.
  • Diameter: The mole is larger than a pencil eraser (about 6 millimeters), though melanomas can be smaller.
  • Evolving: The mole is changing in size, shape, color, or how it feels (itching, bleeding, or becoming raised).

A mole that meets one or more of these criteria does not mean you have melanoma, but it does mean a dermatologist should examine it. Many benign moles can have some of these features. The key is change: a mole you have had for years that suddenly starts to look different is more concerning than a mole that has always looked the same.

Stages and what they mean for prognosis

Melanoma is staged from 0 to IV, with stage 0 being the least advanced and stage IV being the most advanced. Stage 0 (melanoma in situ) means the cancer is confined to the epidermis. Stages I and II are based primarily on thickness: thinner melanomas (less than 1 millimeter) are stage I, while thicker ones without spread to lymph nodes are stage II.

Stage III melanoma has spread to one or more nearby lymph nodes or to skin between the original tumor and the lymph nodes. Stage IV means the cancer has spread to distant organs or distant skin sites. Survival rates differ significantly by stage. For example, the five-year survival rate for stage I melanoma is very high (around 95% or higher), while stage IV melanoma has a much lower survival rate, though newer treatments have improved outcomes in recent years.

Thickness, ulceration (whether the skin over the melanoma is broken), and the presence of mitotic figures (rapidly dividing cells visible under a microscope) also influence staging and prognosis. Your doctor will discuss what your specific stage means for your individual situation.

Risk factors that increase your chance of developing melanoma

Certain characteristics and exposures increase the risk of melanoma. Fair or light skin, particularly skin that burns easily and tans poorly, carries higher risk than darker skin. People with many moles (more than 50) or with atypical moles—moles that are larger, irregularly shaped, or have unusual colors—face elevated risk. A family history of melanoma also increases risk, suggesting both genetic factors and shared sun exposure habits within families.

Severe sunburns, especially during childhood, are a significant risk factor. Intermittent intense sun exposure (such as vacations to sunny climates) appears to carry more risk than chronic daily exposure. Use of indoor tanning beds, particularly before age 30, increases melanoma risk. People with a personal history of melanoma have a higher chance of developing another melanoma later.

Having risk factors does not mean you will develop melanoma. Many people with multiple risk factors never do, while some people with few risk factors do develop it. Risk factors help guide how often you should have skin checks and how carefully you should monitor your own skin.

How melanoma is diagnosed

Diagnosis begins with a clinical examination by a dermatologist, who will look at the suspicious mole or growth using a dermatoscope—a handheld magnifying device that allows detailed viewing of the skin. If the appearance is concerning, the dermatologist will perform a biopsy, removing all or part of the lesion so it can be examined under a microscope by a pathologist.

The pathologist looks for melanoma cells and measures the thickness of the tumor, checks for ulceration, and counts mitotic figures. This microscopic examination confirms whether melanoma is present and provides the information needed to stage it. If melanoma is confirmed, additional imaging—such as ultrasound of nearby lymph nodes or CT scans—may be ordered to determine whether the cancer has spread.

Treatment options depend on stage and thickness

For early-stage melanoma (stages 0, I, and II), surgical excision is the primary treatment. The surgeon removes the melanoma along with a margin of normal skin around it. The width of this margin depends on the thickness of the melanoma; thicker tumors require wider margins. For most early-stage melanomas, this surgery alone is curative.

For stage III melanoma (with lymph node involvement), surgery to remove affected lymph nodes may be recommended, sometimes followed by additional treatment. For stage IV melanoma or melanomas that have recurred, treatment options include immunotherapy drugs (which help the immune system recognize and attack cancer cells), targeted therapy (if the melanoma has specific genetic mutations), or chemotherapy. Newer immunotherapy approaches have significantly improved survival for advanced melanoma in recent years, though outcomes vary by individual.

Frequently Asked Questions

Can you get melanoma from a sunburn?

Severe sunburns, particularly in childhood, increase the risk of developing melanoma later in life. However, a sunburn does not directly cause melanoma the way a burn causes a blister. The damage from UV radiation accumulates over time and can lead to the genetic changes that cause melanoma to develop, sometimes years or decades later.

Is a changing mole always melanoma?

No. Many benign moles change slightly over time—they may darken, lighten, or become slightly raised. However, any mole that changes noticeably in size, shape, color, or texture should be examined by a dermatologist. Most changing moles are not melanoma, but a dermatologist can determine whether evaluation or biopsy is needed.

What is the difference between melanoma and a regular mole?

A regular mole is usually uniform in color, has a smooth border, is symmetrical, and does not change. Melanoma typically has irregular features—asymmetry, uneven borders, multiple colors, or change over time. However, some melanomas can look like regular moles, which is why any mole that concerns you or that changes should be evaluated by a doctor.

If melanoma is caught early, can it be cured?

Early-stage melanoma (stages 0, I, and II) that is completely removed by surgery has a very high likelihood of not returning. However, "cured" is a word doctors use carefully; there is always a small risk of recurrence. People treated for melanoma need regular skin checks and should monitor their skin for new or changing growths throughout their lives.

Can melanoma come back after treatment?

Yes, melanoma can recur even after successful treatment. Recurrence can happen in the skin near the original site, in lymph nodes, or in distant organs. This is why follow-up appointments and regular self-examination are important. The risk of recurrence is higher for thicker melanomas or those that had spread to lymph nodes at diagnosis.