Melanoma is a disease in which malignant (cancer) cells form in melanocytes (cells that color the skin).

The skin is the body’s largest organ. It protects against heat, sunlight, injury, and infection. Skin also helps control body temperature and stores water, fat, and vitamin D. The skin has several layers, but the two main layers are the epidermis (upper or outer layer) and the dermis (lower or inner layer). Skin cancer begins in the epidermis, which is made up of three kinds of cells:

• Squamous cells: Thin, flat cells that form the top layer of the epidermis.
• Basal cells: Round cells under the squamous cells.
• Melanocytes: Cells that make melanin and are found in the lower part of the epidermis. Melanin is the pigment that gives skin its natural color. When skin is exposed to the sun or artificial light, melanocytes make more pigment and cause the skin to darken.

From 2010 to 2019, the number of new cases of melanoma increased by about 1% per year, though the number of deaths each year from melanoma continues to decrease. Melanoma is most common in adults, but it is sometimes found in children and adolescents. For more information, see Childhood Melanoma Treatment.

There are different types of cancer that start in the skin.

There are two main forms of skin cancer: melanoma and nonmelanoma.

Melanoma is a rare form of skin cancer. It is more likely to invade nearby tissues and spread to other parts of the body than other types of skin cancer. When melanoma starts in the skin, it is called cutaneous melanoma. Melanoma may also occur in mucous membranes (thin, moist layers of tissue that cover surfaces such as the lips). This summary is about cutaneous (skin) melanoma and melanoma that affects the mucous membranes.

The most common types of skin cancer are basal cell carcinoma and squamous cell carcinoma. They are nonmelanoma skin cancers. Nonmelanoma skin cancers rarely spread to other parts of the body. For more information, see Skin Cancer Treatment.

Melanoma 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.

When melanoma occurs in the eye, it is called intraocular or ocular melanoma. For more information, see Intraocular (Uveal) Melanoma Treatment.

Unusual moles, exposure to sunlight, and health history can affect the risk of melanoma.

Anything that increases a person's chance of getting a disease is called a risk factor. Not every person with one or more of these risk factors will develop melanoma, and it will develop in some people who don't have any known risk factors. Talk with your doctor if you think you may be at risk.

Risk factors for melanoma include the following:

• Having a fair complexion, which includes the following:
  • Fair skin that freckles and burns easily, does not tan, or tans poorly.
  • Blue or green or other light-colored eyes.
  • Red or blond hair.
• Being exposed to natural sunlight or artificial sunlight (such as from tanning beds).
• Being exposed to certain factors in the environment (in the air, your home or workplace, and your food and water). Some of the environmental risk factors for melanoma are radiation, solvents, vinyl chloride, and PCBs.
• Having a history of many blistering sunburns, especially as a child or teenager.
• Having several large or many small moles.
• Having a family history of unusual moles (atypical nevus syndrome).
• Having a family or personal history of melanoma.
• Being White.
• Having a weakened immune system.
• Having certain changes in the genes that are linked to melanoma.

Being White or having a fair complexion increases the risk of melanoma, but anyone can have melanoma, including people with dark skin.

For more information on risk factors for melanoma, see the following:

• Genetics of Skin Cancer
• Skin Cancer Prevention

Signs of melanoma include a change in the way a mole or pigmented area looks.

These and other signs and symptoms may be caused by melanoma or by other conditions. Check with your doctor if you have any of the following:

• A mole that:
  • changes in size, shape, or color.
  • has irregular edges or borders.
  • is more than one color.
  • is asymmetrical (if the mole is divided in half, the 2 halves are different in size or shape).
  • itches.
  • oozes, bleeds, or is ulcerated (a hole forms in the skin when the top layer of cells breaks down and the tissue below shows through).
• A change in pigmented (colored) skin.
• Satellite moles (new moles that grow near an existing mole).

For pictures and descriptions of common moles and melanoma, see Common Moles, Dysplastic Nevi, and Risk of Melanoma.

Tests that examine the skin are used to diagnose melanoma.

In addition to asking about your personal and family health history and doing a physical exam, your doctor may perform the following tests and procedures to find and diagnose melanoma:

• Skin exam: A doctor or nurse checks the skin for moles, birthmarks, or other pigmented areas that look abnormal in color, size, shape, or texture.
• Biopsy: A procedure to remove the abnormal tissue and a small amount of normal tissue around it. A pathologist looks at the tissue under a microscope to check for cancer cells. It can be hard to tell the difference between a colored mole and an early melanoma lesion. Patients may want to have the sample of tissue checked by a second pathologist. If the abnormal mole or lesion is cancer, the sample of tissue may also be tested for certain gene changes.

  There are four main types of skin biopsies. The type of biopsy done depends on where the abnormal area formed and the size of the area.

  • Shave biopsy: A sterile razor blade is used to “shave-off” the abnormal-looking growth.
  • Punch biopsy: A special instrument called a punch or a trephine is used to remove a circle of tissue from the abnormal-looking growth.
  • Incisional biopsy: A scalpel is used to remove part of a growth.
  • Excisional biopsy: A scalpel is used to remove the entire growth.

Certain factors affect prognosis (chance of recovery) and treatment options.

The prognosis and treatment options depend on the following:

• The thickness of the tumor and where it is in the body.
• How quickly the cancer cells are dividing.
• Whether there was bleeding or ulceration of the tumor.
• How much cancer is in the lymph nodes.
• The number of places cancer has spread to in the body.
• The level of lactate dehydrogenase (LDH) in the blood.
• Whether the cancer has certain mutations (changes) in a gene called BRAF.
• The patient’s age and general health.