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Medical Description

Most skin cancer begins in the epidermis.

The skin is the largest organ of the body. It protects the body from infection and all sorts of environmental insults, and prevents the loss of too much water and other fluids. The skin sends messages to the brain about heat, cold, touch and pain sensations.

Skin layersThe top layer of the skin is called the epidermis. It protects the deeper layers of skin and the organs. The epidermis has several layers. Cells divide in the basal (bottom layer) and then migrate upward to the skin's surface, where they eventually fall off in flakes.

Most skin cancer begins in the epidermis. The epidermis consists of two main types of cells: keratinocytes and melanocytes. Keratinocytes make up the vast majority of cells and contribute to most of its function. Melanocytes produce melanin, the pigment that gives skin its colour. Only a small number of melanocytes are necessary to produce enough pigment for the entire epidermis.

A melanoma is a tumour that develops from abnormalities in melanocytes. Melanoma tumours are often brown or black because most melanoma cells still produce melanin (colouring). A melanoma usually appears as an irregularly shaped mole that may contain several different shades of brown and black. For more about identifying possible melanomas, see our pages on early detection.

Melanoma is much less common than basal and squamous cell skin cancers, which develop from keratinocyte cells, but it is often more serious. The number or rate of all skin cancers is rising, and especially among young women.

Melanoma is almost always curable in its early stages, making early detection crucial. If left untreated, melanoma can spread (metastasize) to other parts of the body, including the liver, lungs or brain.

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Melanoma Skin Cancer

  • A publication of:
  • Women's College Hospital