Melanoma and Other Skin Cancers - Introduction

Introduction

Skin cancer is cancer that starts in the skin cells. Skin cancers are divided into two major groups:

• Nonmelanoma, which includes basal cell cancer and squamous cell cancer
• Melanoma, the deadliest form of skin cancer

Different skin cancers start in different cells of the skin. To understand how skin cancer develops, it is useful to understand the structure of the skin.

The skin is the largest organ in the body and consists of layers.

• The outermost layer of the skin is called the epidermis. It is only about 20 cells deep, roughly as thick as a sheet of paper.
• The dermis ranges in thickness from 1 - 4 millimeters (about 1/32 - 1/8 inch). The dermis contains tiny blood and lymph vessels, which increase in number deeper in the skin.

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Melanocytes. A layer of cells between the epidermis and the dermis called melanocytes produces a brown-black skin pigment (melanin) that determines skin and hair color. Melanin also helps protect against the damaging rays of the sun.

As a person ages, melanocytes often spread (proliferate). They form clusters that appear on the skin surface as small, dark, flat, or dome-shaped spots, which are usually harmless moles or “liver spots."

• When cell proliferation occurs in a controlled and contained manner, the resulting spot is noncancerous (benign) and is commonly referred to as a mole or nevus.
• Sometimes, however, pigment cells grow out of control and become a cancerous and life-threatening melanoma.

Click the icon to see an image of melanin.

Review Date: 07/04/2010
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).