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Skin Cancer

Skin Cancer Overview

The skin is the largest organ in the body. Skin cancer is the most common of all human cancers. Some form of skin cancer is diagnosed in more than 1 million people in the United States each year.

Cancer occurs when normal cells undergo a transformation during which they grow abnormally and multiply without normal controls.

  • As the cells multiply, they form a mass called a tumor. Tumors of the skin are often referred to as skin lesions.
  • Tumors are said to be cancerous only if they are composed of malignant cells. This means that they encroach on and invade neighboring tissues because of their uncontrolled growth.
  • Tumors may also travel to remote organs via the bloodstream or lymphatic system.
  • This process of invading and spreading to other organs is called metastasis.
  • Tumors overwhelm surrounding tissues by invading their space and taking the oxygen and nutrients the normal cells need to survive and function.

Skin cancers are of three major types: basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma.

  • The vast majority of skin cancers are BCCs or SCCs. While malignant, these are unlikely to spread to other parts of the body. They may be locally disfiguring if not treated early.
  • A small but significant number of skin cancers are malignant melanomas. Malignant melanoma is a highly aggressive cancer that tends to spread to other parts of the body. These cancers may be fatal if not found and treated early.

Like many cancers, skin cancers start as precancerous lesions. These precancerous lesions are changes in skin that are not cancer but could become cancer over time. Medical professionals often refer to these changes as dysplasia. Some specific dysplastic changes that occur in skin are as follows:

  • Actinic keratosis is a patch of red or brown, scaly, rough skin, which can develop into squamous cell carcinoma.
  • A nevus is a mole, and dysplastic nevi are abnormal moles. These can develop into melanoma over time.

Moles (nevi) are simply growths on the skin. They are very common. Very few moles become cancer.

  • Most people have 10-40 moles on their body.
  • Moles can be flat or raised; some begin as flat and become raised over time.
  • The surface is usually smooth.
  • Moles are round or oval and no larger than ¼-inch across.
  • Moles are usually pink, tan, brown, or the same color as the skin. Other colors are sometimes noted.
  • An individual's moles usually look pretty much alike. A mole that looks different from the others should be examined by your health-care provider.

Dysplastic nevi are not cancer, but they can become cancer.

  • People with dysplastic nevi often have a lot of them, perhaps as many as 100 or more.
  • People with many dysplastic nevi are more likely to develop melanoma, either within an existing nevus or on an area of normal skin.
  • Dysplastic nevi are usually irregular in shape, with notched or fading borders.
  • Dysplastic nevi may be flat or raised, and the surface may be smooth or rough ("pebbly").
  • Dysplastic nevi are often large, ¼-inch across or even larger.
  • Dysplastic nevi are typically of mixed color, including pink, red, tan, and brown.

Recent studies demonstrate that the number of skin cancer cases in the United States is growing at an alarming rate. Fortunately, increased awareness on the part of Americans and their health-care providers has resulted in earlier diagnosis and improved outcomes.

Medically Reviewed by a Doctor on 6/11/2014
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Read What Your Physician is Reading on Medscape

Skin Cancer: Melanoma »

Despite recent declines in the incidence and mortality of cancer overall, the incidence of cutaneous melanoma continues to escalate.

Read More on Medscape Reference »


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