About the skin

The skin is the largest organ in the body. It protects against infection and injury and helps regulate body temperature. The skin also stores water and fat and produces vitamin D.

The skin is made up of three main layers:

  • The epidermis. The outer layer of skin

  • The dermis. The inner layer of skin

  • The hypodermis. The deep layer of fat

See the Medical Illustrations section for a drawing of these layers.

About melanoma

The deepest layer of the epidermis, located just above the dermis, contains cells called melanocytes, which produce the skin’s pigment or color. Melanoma begins when healthy melanocytes change and grow uncontrollably, forming a cancerous tumor. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body. Sometimes, melanoma develops from a normal mole a person already has on their skin.

Melanoma occurs most often on the skin of men’s backs or on women’s legs, but melanoma can develop anywhere on the body, including the head and neck, the skin under the fingernails, genitals, and even the soles of the feet or palms of the hands. Melanoma may not have the color of a mole. It may have no color or be slightly red, which is called amelanocytic melanoma.

When found early, melanoma can often be cured with surgery. However, melanoma is the most serious form of skin cancer. It can grow deep into the skin, called invasive melanoma. It can also invade lymph nodes and blood vessels and spread to distant parts of the body.

Normal Skin Tissue

Normal Skin TissueClick to Enlarge

These images used with permission by the College of American Pathologists.

This section focuses on cutaneous melanoma, which is melanoma that develops on the skin. Melanoma can also develop in the mucous membranes that line the mouth, gastrointestinal tract, a woman’s vagina, and other locations around the body. Melanoma may also develop in the eye. You can learn more about melanoma diagnosed in other parts of the body, such as melanoma of the eye, melanoma of the anus, and melanoma of the vagina, in these specific cancer type sections. For information about other types of skin cancer, review the section on basal cell and squamous cell skin cancers.

Looking for More of an Overview?

If you would like additional introductory information, explore these related items. Please note these links will take you to other sections on Cancer.Net:

  • ASCO Answers Fact Sheet: Read a one-page fact sheet (available as a PDF) that offers an easy-to-print introduction to this type of cancer.

  • Cancer.Net Patient Education Video: View a short video led by an ASCO expert in this type of cancer that provides basic information and areas of research.