Cancer is a disease in which cells grow in an abnormal way. Normally, the cells divide in a controlled manner 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 tumors invade and damage tissue around them. The cancer cells can also enter the lymph and blood streams, spreading to other parts of the body. Melanoma is skin cancer of the melanocytes, the cells that produce skin color and give moles their dark color. Melanoma tends to be an aggressive type of skin cancer. It is also more likely to spread to other parts of the body.

Cancer Cell Growth

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There are 2 main layers of the skin:

  • Epidermis—The thinnest, outermost layer. The epidermis is made of different cell types and has 5 separate layers. There are no blood vessels or nerves directly in the epidermis. Melanocytes can be found in the deepest layer of the epidermis all over the body.
  • Dermis—The dermis is a layer of connective tissue under the epidermis. It is thicker and contains blood vessels, nerves, immune cells, hair follicles, and sweat and oil glands. The dermis is made up of 2 layers of different cell types.

Layers of the Skin

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Melanocytes appear on the surface of the skin as moles. Most moles are harmless but some may be develop into melanoma. Because melanomas are the bottom layer of the epidermis they can quickly grow down into the dermis. In the dermis the cancer has access to lymph nodes and blood vessels, which then carry cancer cells to other parts of the body. The most common sites for melanoma to spread to are the lungs, liver, brain, bones, and intestinal tract.

Males tend to get melanoma on the torso, the area between the shoulders and hips. Women are more likely to find melanoma on the arms or legs. It is important to note that melanoma can develop anywhere on the body, even those not regularly exposed to the sun, like the genitals, anal area, eyes, or mouth.

Melanoma is categorized by where tumors start, how they grow, and their appearance under a microscope. Four basic types of melanoma include:

  • Superficial spreading—This is the most common type of melanoma. Grows on superficial layers of skin for an period of time before it gets deeper. Appears as discolored patch, may develop in previously benign mole. Most common in young people.
  • Nodular—Usually invasive at diagnosis. Often noticed as a bump that is often black, but may be other colors or skin tone.
  • Acral lentiginous—This is the most common type found in those of Asian, Hispanic, or African descent. Most often appears as discoloration under fingernail or toenail, on palms of the hands, or soles of the feet.
  • Lentigo maligna—Also starts as superficial. Often starts as flat or mildly raised discolored patch. More common in older adults on frequently sun exposed skin.

Melanoma of the Skin

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This fact sheet focuses on melanomas that affect the skin.