Understand melanoma, a kind of skin cancer

Melanoma, a rare form of skin cancer, can be dangerous. It is more likely than other, more common, types of skin cancer to invade nearby tissues and spread to other parts of the body. Other more common types of skin cancer include basal cell carcinoma and squamous cell carcinoma of the skin. These nonmelanoma skin cancers rarely spread to other parts of the body.

The information below is primarily based on information originally published by the National Cancer Institute (NCI), the US government’s main agency for cancer research. It may help you gain a better understanding of your melanoma diagnosis and what may be happening to your body. This may help when making important decisions with your doctor.

What is melanoma?

Melanoma is a disease in which malignant (cancer) cells form from melanocytes (cells that color the skin). This type of cancer can occur anywhere on the skin. In men, melanoma is often found on the trunk (the area from the shoulders to the hips) or the head and neck. In women, melanoma forms most often on the arms and legs.

Unusual moles, exposure to sunlight, and health history can affect the risk of melanoma. Being White or having a fair complexion increases the risk of melanoma, but anyone can develop melanoma, including people with dark skin.

Stages of melanoma

Melanoma is categorized in 5 stages ranging from 0 to 4, with stage 4 being the most severe. The stages can also be broken down further into substages (A, B, C, or D).

Stage 0 melanoma

In stage 0, abnormal melanocytes are found in the epidermis (outer layer of the skin). These abnormal melanocytes may become cancer and spread into nearby normal tissue. Stage 0 is also called melanoma in situ.

Stage 1 melanoma

In stage 1, cancer has formed and there are no signs of cancer beyond the main tumor. Stage 1 is divided into stages 1A and 1B.

Stage 1A

The tumor is up to 1 millimeter thick (about the size of a sharpened pencil point), with or without ulceration (a breakdown of the skin).

Stage 1B

The tumor is more than 1 but not more than 2 millimeters thick (about the size of a new crayon point), without ulceration.

Stage 2 melanoma

Stage 2 is divided into stages 2A, 2B, and 2C. In stage 2 melanoma, there are no signs of cancer beyond the main tumor.

Stage 2A

The tumor is more than 1 but not more than 2 millimeters thick (1 millimeter is about the size of a sharpened pencil point, 2 millimeters is about the size of a new crayon point), with ulceration (a breakdown of the skin).

Or stage 2A can be

The tumor is more than 2 but not more than 4 millimeters thick, without ulceration.

Stage 2B

The tumor is more than 2 but not more than 4 millimeters thick, with ulceration.

Or stage 2B can be

The tumor is more than 4 millimeters thick, without ulceration.

Stage 2C

The tumor is more than 4 millimeters thick, with ulceration.

Stage 3 melanoma

Stage 3 is divided into stages 3A, 3B, 3C, and 3D.

Stage 3A

The tumor is not more than 1 millimeter thick (about the size of a sharpened pencil point), with ulceration (a breakdown of the skin), or not more than 2 millimeters thick (about the size of a new crayon point), without ulceration. Cancer is found in 1 to 3 lymph nodes by sentinel lymph node biopsy (a surgical procedure to see if the cancer has spread).

Stage 3B

(1) It is not known where the cancer began or the primary tumor can no longer be seen, and one of the following is true:
- cancer is found in 1 lymph node by physical exam or imaging tests; or
- there are microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin (all of these terms refer to a small group of tumor cells near the original tumor or growing between the original tumor and a lymph node).

Or stage 3B can be

(2) The tumor is not more than 1 millimeter thick, with or without ulceration, or not more than 2 millimeters thick, without ulceration, and one of the following is true:
- cancer is found in 1 to 3 lymph nodes; or
- there are microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin.

Or stage 3B can be

(3) The tumor is more than 1 but not more than 2 millimeters thick, with ulceration, or more than 2 but not more than 4 millimeters thick, without ulceration, and one of the following is true:
- cancer is found in 1 to 3 lymph nodes; or
- there are microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin.

Stage 3C

(1) It is not known where the cancer began, or the primary tumor can no longer be seen. Cancer is found:
- in 2 or 3 lymph nodes; or
- in 1 lymph node and there are microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin; or
- in 4 or more lymph nodes, or in any number of lymph nodes that are matted (clumped) together; or
- in 2 or more lymph nodes and/or in any number of lymph nodes that are matted together; and there are microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin.

Or stage 3C can be

(2) The tumor is not more than 2 millimeters thick, with or without ulceration, or not more than 4 millimeters thick, without ulceration. Cancer is found:
- in 1 lymph node and there are microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin; or
- in 4 or more lymph nodes, or in any number of lymph nodes that are matted together; or
- in 2 or more lymph nodes and/or in any number of lymph nodes that are matted together; and there are microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin.

Or stage 3C can be

(3) The tumor is more than 2 but not more than 4 millimeters thick, with ulceration, or more than 4 millimeters thick, without ulceration. Cancer is found in 1 or more lymph nodes and/or in any number of lymph nodes that are matted together; and there may be microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin.

Or stage 3C can be

(4) The tumor is more than 4 millimeters thick, with ulceration, and:
- the cancer is found in 1 or more nearby lymph nodes, and/or
- there are microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin.

Stage 3D

The tumor is more than 4 millimeters thick, with ulceration. Cancer is found:
- in 4 or more lymph nodes, or in any number of lymph nodes that are matted together; or
- in 2 or more lymph nodes and/or in any number of lymph nodes that are matted together; and there are microsatellite tumors, satellite tumors, and/or in-transit metastases on or under the skin.

Learn about a possible treatment option that may help prevent melanoma from coming back after surgery.

Stage 4 melanoma

In stage 4, the cancer has spread to other parts of the body, such as the lung, liver, brain, spinal cord, bone, soft tissue (including muscle), gastrointestinal (GI) tract, and/or distant lymph nodes. Cancer may have spread to places in the skin far away from where it first started.

Learn about a possible treatment option for certain patients with advanced melanoma that has spread or can’t be removed by surgery.

What’s next

Common cancer treatments

Be involved in treatment decisions

Who is on your care team

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