Melanoma is the most deadly form of skin cancer, although it can often be cured if caught very early. To understand how melanomas form, it is useful to know something about the skin.

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

  • The outermost layer of the skin, the epidermis, is only about 20 cells deep, roughly as thick as a sheet of paper.
  • The dermis ranges in thickness from one to four millimeters (about 1/32 to 1/8 inch). The dermis contains tiny blood and lymph vessels, which increase in number deeper in the skin.
Skin layers picture
The skin is the largest organ of the body. The skin and its derivatives (hair, nails, sweat, and oil glands) make up the integumentary system. One of the main functions of the skin is protection. It protects the body from external factors such as bacteria, chemicals, and temperature. The skin contains secretions that can kill bacteria, and the pigment melanin provides a chemical pigment defense against ultraviolet light that can damage skin cells. The skin also helps control body temperature.

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

Melanoma. Melanocytes give melanoma its name. As a person ages, melanocytes often proliferate, forming concentrated clusters that appear on the 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 lesion is benign and is commonly referred to as a mole or nevus. Most adults have at least several dozen benign moles.
  • Sometimes, however, pigment cells grow out of control and become a malignant and life-threatening melanoma.
Melanoma And Other Skin Cancers picture

Click the icon to see an image of melanin.

At first, melanoma cells grow sideways (laterally), and so are confined to the epidermis and to the top layers of the dermis. However, once they grow downward into the dermis, the cancer will come into contact with lymph and blood vessels. The thicker the melanoma, the greater the likelihood that it could spread through these vessels to distant sites. Removal of the lesion before it penetrates to the deeper layers of the skin is crucial for achieving a cure. Early detection is very important.

Significant Features

People who regularly check moles on their skin may have a lower risk of developing advanced melanoma, but people should not panic over every skin irregularity. A doctor should examine any suspicious lesion with one or more of the features discussed below or that changes noticeably in size, color, or shape. Itching, tenderness, scaling, bleeding, crusting, or sores can signal potentially cancerous changes in any mole.

A mnemonic device, ABCDE, is used to describe several features that help to distinguish melanomas from noncancerous growths:

  • Asymmetry (A). About half the time, a melanoma develops in an existing mole; in other cases, it arises as a new lesion that can resemble an ordinary mole. A noncancerous mole, however, is generally symmetric and circular in shape, while melanoma usually grows in an irregular, asymmetric fashion.
  • Border Irregularity (B). Benign lesions generally have clearly defined borders that mark the boundary between mole and skin. A melanoma, in contrast, often has notched or indistinct borders that may signal ongoing growth and spread of the cancer.
  • Color Variation (C). One of the earliest signs of melanoma may be the appearance of various colors within the lesion. Because melanomas arise within pigment-forming cells, they are often varicolored lesions of tan, dark brown, or black, reflecting the production of melanin pigment at different depths within the skin. Occasionally, lesions are flesh colored or surrounded by redness or lighter areas of depigmentation. Pink or red areas may result from inflammation of blood vessels within the skin; blue areas reflect pigment in the deeper layers of the skin; and white areas can arise from dead cancerous tissue.
  • Diameter (D). A diameter of 6 millimeters or larger (about the size of a pencil eraser) is worrisome. Melanomas start out small; by the time a lesion has grown this large, other abnormalities will most likely be present. No matter what size, a doctor should examine any suspicious lesion.
  • Evolution (E). A lesion that is growing or changing deserves evaluation.

While the ABCDE plan is a general guide for melanoma detection, it will not help detect the early stages of nodular melanoma. This type of melanoma is generally symmetrical, has regular borders, and may be solid black, blue-black or pink. It may also miss amelanotic melanoma, which is not pigmented.

You should keep in mind that the most important warning sign of melanoma is a new or changingskin lesion, regardless of size or color. Changes that occur over a short period of time (particularly over a few weeks) are most worrisome.

Growth Pattern

Melanomas tend to grow in stages:

  • Most melanomas tend to be flat initially and spread laterally across the skin surface as they grow. At this early stage, which can last from 1 to 5 years or longer, removal of the growth has an excellent chance of curing the melanoma. Still, there is a chance that some of these melanomas are invasive, and they should be treated aggressively.
  • Lesions that become raised or dome-shaped over at least part of their surface indicate that downward growth has occurred. In some cases, this growth is very rapid, occurring over a period of weeks to months.

Any suspicious lesion should be checked immediately, particularly if it has grown quickly or is partially flat and partially raised.

Location

Common sites of melanoma in men are the head, neck, and trunk; and in women, the arms or legs. Any area of the skin may be affected, however, in either gender. You may not notice melanomas if they appear on areas that are difficult to examine, such as the scalp or the back. Less common sites for melanoma include the fingers, palms, soles of the feet, the genitals, lips, or under the fingernails or toenails. The presence of a dark lesion under the nail that runs into the adjoining skin and doesn't heal may signal melanoma. Rarely, melanomas appear in the mouth, in the iris of the eye, or in the retina at the back of the eye, where they may be detected during dental or eye examinations.

Melanoma And Other Skin Cancers picture

Click the icon to see an image of melanoma.

Specific Melanomas

Superficial Spreading Melanoma. Superficial spreading melanoma is the most common and most curable. It is flat, asymmetrical, unevenly colored, and usually grows outward across the surface of the skin.

Nodular Melanoma. Nodular melanoma appears as a fast-growing brown or black lump, and its characteristics do not always fit the definitions described above. It is important to check for this type of melanoma, because it is associated with an outbreak of other tumors.

Lentigo Maligna. Lentigo maligna (sometimes called Hutchinson's freckle) usually occurs in elderly people and is marked by flat, mottled, tan-to-brown freckle-like spots with irregular borders. These lesions often appear on the face or other sun-exposed areas and typically enlarge slowly for 5 to 15 years before cancer appears.

Acral Lentiginous Melanoma. Although rare, acral lentiginous melanoma is the most common melanoma among African and Asian populations. It commonly appears as a dark patch on the palms, soles, fingers, toes, under fingernails or toenails, or mucous membranes.