This page was reviewed under our medical and editorial policy by
Maurie Markman, MD, President, Medicine & Science
This page was updated on May 27, 2022.
Though melanoma is a relatively rare form of skin cancer, about 100,640 new cases are expected to be diagnosed in 2024, the American Cancer Society estimates. About 1 percent of skin cancers are melanomas—most others are basal cell and squamous cell skin cancers—but melanomas make up a majority of skin cancer deaths.
Before recommending treatment, doctors first need to learn more about the melanoma and what’s going on inside the skin.
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Once doctors have collected all the information they can about the cancer, they will assign a stage. The stage gives doctor and patient a common language to understand how advanced the cancer is, where it’s located and which treatment options are available.
Melanoma in situ means that there are melanocyte cells that may turn cancerous on the skin. This is early stage melanoma—it’s best to catch and treat melanocytes here before they have the chance to turn cancerous.
In general, a stage 1 melanoma has grown deeper into the skin but hasn’t spread to the lymph nodes or other parts of the body.
Stage 1A melanoma: The cancer isn’t more than 1 millimeter (mm) thick, with or without ulceration.
Stage 1B melanoma: The tumor is more than 1 mm thick, but not more than 2 mm thick, without ulceration.
A stage 2 melanoma has grown deeper into the skin and has more high-risk features, but it hasn’t spread.
Stage 2A melanoma: The tumor is either more than 1 mm but not more than 2 mm thick, with ulceration, or more than 2 mm but not more than 4 mm thick, without ulceration.
Stage 2B melanoma: The tumor is more than 2 mm but not more than 4 mm thick, with ulceration, or more than 4 mm thick, without ulceration.
Stage 2C melanoma: The tumor is more than 4 mm thick, with ulceration. A melanoma with a thickness greater than 4 mm has a high risk of spreading.
Stage 3 and stage 4 melanomas are considered advanced melanomas.
A stage 3 melanoma diagnosis means that the cancer cells have spread to nearby lymph nodes, but not to distant organs or any other part of the body.
In stage 4 melanoma, the cancer has spread to other organs and/or distant lymph nodes. Though it all falls within stage 4 cancer, the M of the TNM system may indicate where the cancer has spread specifically, such as to other areas of the skin (M1A), the lung (M1B), other organs or areas of the body (M1C), or—at its most advanced—the central nervous system (M1D).
The melanoma staging process can be complex. Stages are assigned based on the size or thickness of the tumor, whether or not it has spread to the lymph nodes or other organs, and certain other characteristics such as growth rate.
The melanoma stages range from 1 through 4, with higher numbers indicating more advanced melanoma. Some stage numbers are followed by the capital letters A through D to further describe the tumor and its potential spread.
The American Joint Committee on Cancer has developed a uniform staging system that allows the care team to determine how advanced a melanoma is, and to share that information with each other in a meaningful way.
This melanoma staging system, known as TNM staging, measures three characteristics of the cancer.
T (tumor): Describes the tumor’s thickness, or how deep it has grown into the skin. The thickness of the melanoma, also known as the Breslow measurement, is an important factor in predicting whether or not a tumor has spread. The thicker the melanoma, the greater the chance of it spreading. The rate at which the tumor cells are dividing (also known as the mitotic rate) and the presence or absence of ulceration (an open, bleeding sore) are also considered in determining the T category.
N (node): Indicates whether or not the melanoma has spread to nearby lymph nodes, or the channels connecting the lymph nodes.
M (metastasis): Refers to whether or not the melanoma has spread to distant organs, as well as on levels of lactate dehydrogenase (LDH), a substance in the blood. In other words, if it has metastasized.
The TNM categories also have subtypes.
Tumor thickness (T)
Lymph node involvement (N): The higher the number after the N, the more lymph nodes that contain cancer.
Metastasis (M): Melanoma may spread almost anywhere, but it tends to travel to the lungs, liver, brain, bones and the skin or lymph nodes in other parts of the body. The letter M indicates the potential spread of the melanoma throughout the body.
To add to the complexity of staging, the cancer also may have a clinical stage and a pathologic stage.
Clinical staging takes place before surgery, based on blood tests, physical exams or imaging tests such as X-rays, a computed tomography (CT) scan, magnetic resonance imaging (MRI) or positron emission tomography (PET) scans.
What the care team discovers during surgery may provide more detailed information about the cancer’s size and spread. Often, some tissue from the surgery is examined afterward to provide more clues. This process is known as pathologic staging, or surgical staging.
If surgery isn’t possible, the care team will use the clinical stage when determining a treatment plan.
A relapse of melanoma within 2 centimeters of the original tumor site is considered a local recurrence. Lymph node recurrence and distant recurrence are terms used to describe cancer that has the same DNA characteristics as the original tumor but develops elsewhere in the body, such as the lymph nodes.
Lymph node recurrence develops in the lymph node(s) in the area nearest the original melanoma tumor. It’s considered distant recurrence when melanoma cells enter the bloodstream and develop into tumors at another location in the body. Once they enter the circulatory system, melanoma cancer cells may travel to distant sites. They may develop in any tissue, but they typically grow in the lungs, liver or brain. Metastases may also occur in the bone, heart, pancreas, kidneys or thyroid, among other locations.
One way to estimate life expectancy when battling cancer is to consider the five-year relative survival rate for that disease. A five-year relative survival rate suggests the likelihood that a person with a specific type and stage of cancer would live for at least five years after the diagnosis, compared with people who don't have that cancer type. The rate includes the life expectancy of patients who are still in treatment and those who have finished treatment and have had tests that show no evidence of disease.
The American Cancer Society reports the following melanoma relative survival rates:
Localized melanoma: If the cancer hasn't spread outside the area of the skin where it originated, the five-year relative survival rate is 99 percent.
Regional melanoma: For patients with melanoma that's spread to nearby lymph nodes or structures, the five-year relative survival rate is 71 percent.
Distant melanoma: If the cancer has spread to distant organs or body parts (like the lungs or liver), the five-year relative survival rate is 32 percent.