Cancer is a disease in which cells grow in an abnormal way. They are supposed to divide in a controlled way to replace old or damaged cells. If the cells keep dividing when new ones are not needed, a mass of tissue called a tumor forms.

Not all tumors are cancer, those that are cancer are called malignant. Cancer grows and harms the tissue around them. Melanoma is a type of skin cancer that starts in the cells that give skin and moles their color. They are called melanocytes. Melanoma is less common than other skin cancer types. But, it is the most likely to grow and spread.

Cancer Cell Growth
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Normal Anatomy and the Development of Melanoma

There are 2 main layers of the skin:

  • Epidermis—The thinnest, outermost layer of skin. There are no blood vessels or nerves in its 5 layers. Melanocytes are in the deepest layer all over the body.
  • Dermis—The dermis lies under the epidermis. It is thicker and has blood vessels, nerves, and lymph tissue. There are 2 dermis layers.
Layers of the Skin
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The skin is covered with moles. The amount differs from person to person. Most moles are harmless, but some can turn cancerous. Melanomas start at the the bottom layer of the epidermis. This means they can quickly grow downward into the dermis. Cancer can spread to the lymph nodes and blood vessels in the dermis, then to the rest of the body. The most common sites for melanoma to spread are the lungs, liver, brain, bones, and the intestines.

Males tend to get melanoma between the shoulders and hips. Women are more likely to find it on the arms or legs. But, melanoma can start in any mole anywhere on the body such as the genitals, eyes, or under the nails.

Types of Melanoma

Melanoma is grouped by where tumors start, how they grow, and how they look in a lab. Basic types are:

  • Superficial spreading—This is the most common type (also the most common in young people). It grows on the top layers for a time before it gets deeper. It looks like a discolored patch and can start in a previously harmless mole.
  • Nodular—Often noticed as a bump that is often black or with an ulcer. This type tends to be more harmful.
  • Acral lentiginous—This is the most common type found in those of who are Black, Asian, or Hispanic. It may start as discoloration under fingernail or toenail, on palms of the hands, or soles of the feet.
  • Lentigo maligna—Often starts as flat or mildly raised discolored patch. More common in older adults on skin that is often exposed to the sun.
  • Ocular—A rare type that starts in the eye.
Melanoma of the Skin
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This fact sheet focuses on melanomas of the skin.

This fact sheet focuses on melanomas of the skin.

What are the risk factors for melanoma?What are the symptoms of melanoma?How is melanoma diagnosed?What are the treatments for melanoma?Are there screening tests for melanoma?How can I reduce my risk of melanoma?What questions should I ask my doctor?What is it like to live with melanoma?Where can I get more information about melanoma?

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