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Melanoma Skin Cancer
What You Need to Know â" Now
By American Cancer Society
American Cancer Society / Health PromotionsCopyright © 2012 American Cancer Society
All rights reserved.
Your Melanoma Skin Cancer
What Is Cancer?
The body is made up of hundreds of millions of living cells. Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person's life, normal cells divide faster to allow the person to grow. After the person becomes an adult, most cells divide only to replace worn-out or dying cells or to repair injuries.
Cancer begins when cells in a part of the body start to grow out of control. There are many kinds of cancer, but they all start because of out-of-control growth of abnormal cells. Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells continue to grow and form new, abnormal cells. Cancer cells can also invade (grow into) other tissues, something that normal cells cannot do. Growing out of control and invading other tissues are what makes a cell a cancer cell.
Cells become cancer cells because of damage to DNA. DNA is in every cell and directs all its actions. In a normal cell, when DNA is damaged, the cell either repairs the damage or the cell dies. In cancer cells, the damaged DNA is not repaired, but the cell does not die like it should. Instead, this cell goes on making new cells that the body does not need. These new cells will all have the same damaged DNA as the first cell.
People can inherit damaged DNA, but most DNA damage is caused by mistakes that happen while the normal cell is reproducing or by something in the environment. Sometimes the cause of the DNA damage is something obvious, like cigarette smoking. Often, however, no clear cause is found.
In most cases, the cancer cells form a tumor. Some cancers, such as leukemia, rarely form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues where they grow.
Cancer cells often travel to other parts of the body, where they begin to grow and form new tumors that replace normal tissue. This process is called metastasis. It happens when the cancer cells get into the bloodstream or lymph vessels of the body.
No matter where a cancer may metastasize, or spread, it is always named for the place where it started. For example, breast cancer that has spread to the liver is still called breast cancer, not liver cancer. Likewise, prostate cancer that has spread to the bone is metastatic prostate cancer, not bone cancer.
Different types of cancer can behave very differently. For example, lung cancer and breast cancer are very different diseases. They grow at different rates and respond to different treatments. That is why people with cancer need treatment that is aimed at their particular kind of cancer.
Not all tumors are malignant. Tumors that are not cancer are called benign. Benign tumors can cause problems — they can grow very large and press on healthy organs and tissues. However, they cannot invade other tissues. Because they cannot invade other tissues, they also cannot metastasize, or spread, to other parts of the body. These tumors are almost never life threatening.
What Is Melanoma?
Melanoma is a cancer that starts in a certain type of skin cell. To understand melanoma, it helps to know about the normal structure and function of the skin.
Skin is the largest organ in your body. It does several different things:
covers the internal organs and protects them from injury
serves as a barrier to germs such as bacteria
prevents the loss of too much water and other fluids
helps control body temperature
The skin has the following 3 layers:
The top layer of skin is the epidermis. The epidermis is very thin, averaging only 0.2 millimeters (mm) thick (about 1/100 of an inch). It protects the deeper layers of skin and the organs of the body from the environment.
Keratinocytes are the main cell type of the epidermis. These cells make an important protein called keratin, which gives the skin strength and flexibility and makes the skin waterproof.
The epidermis itself is made up of 3 sublayers. The outermost part of the epidermis is called the stratum corneum, or horny layer. It is composed of dead keratinocytes that are continually shed as new cells form. The cells in this layer are called squamous cells because of their flat shape.
Just below the stratum corneum are living keratinocytes. Below that is the basal layer, the inner layer of the epidermis. The cells of the basal layer, called basal cells, continually divide to form new keratinocytes. These new keratinocytes replace the older keratinocytes that slough off the skin's surface.
Melanocytes, the cells that can become melanoma, are also present in the epidermis. These skin cells make the brown pigment called melanin, which makes skin tan or brown. Melanin protects the deeper layers of the skin from some of the harmful effects of the sun.
The epidermis is separated from the deeper layers of skin by the basement membrane. The basement membrane is an important structure. When a cancer becomes more advanced, it generally grows through the basement membrane.
The middle layer of the skin is called the dermis. The dermis is much thicker than the epidermis. It contains hair follicles, sweat glands, blood vessels, and nerves that are held in place by a protein called collagen. Collagen is made by cells called fibroblasts and gives the skin its resilience and strength.
The deepest layer of the skin is called the subcutis. The subcutis and the lowest part of the dermis form a network of collagen and fat cells. The subcutis helps the body conserve heat and has a shock-absorbing effect that helps protect the body's organs from injury.
Benign Skin Tumors
Many types of benign (noncancerous) tumors can develop from different types of skin cells.
A mole, or nevus, is a benign skin tumor that develops from melanocytes. Nearly all moles are harmless, but having some types may raise your risk of melanoma. See the section "What Are The Risk Factors for Melanoma?" on page 11 for more information about moles.
A Spitz nevus is a kind of skin tumor that sometimes looks like melanoma. These tumors are generally benign and do not spread. However, sometimes doctors have trouble telling Spitz nevi from true melanomas, even when looking at them under a microscope. Therefore, they are often removed, just to be safe.
Other benign tumors
Benign tumors that develop from other types of skin cells include the following:
seborrheic keratoses: tan, brown, or black raised spots with a "waxy" texture or rough surface
hemangiomas: benign blood vessel growths often called cherry or strawberry spots or port wine stains
lipomas: soft growths of benign fat cells
warts: rough-surfaced growths caused by a virus
Most of these tumors rarely, if ever, develop into cancers. There are a lot of other kinds of benign skin tumors, but most are not very common.
Melanoma is a cancer that begins in the melanocytes. Other names for this cancer include malignant melanoma and cutaneous melanoma. Because most melanoma cells still produce melanin, melanoma tumors are usually brown or black. This is not always true, however, as melanomas can be non-pigmented (without color).
Melanomas can occur anywhere on the skin but are more likely to start in certain locations. The trunk (chest and back) is the most common site in men. The legs are the most commonly affected site in women. The neck and face are other common sites for both men and women.
Having darkly pigmented skin lowers your risk, but it is not a guarantee — anyone can get melanoma. Melanoma can develop on the palms of the hands, the soles of the feet, and under the nails. Melanomas in these areas represent more than half of all melanomas in blacks but fewer than 10% of melanomas in whites.
Melanomas can form in other parts of the body such as the eyes, mouth, and vagina, but melanomas in these locations are much less common than melanoma of the skin. For more information about melanomas in these organs, contact the American Cancer Society at 800-227-2345, or visit our Web site, cancer.org.
Melanoma is much less common than basal cell and squamous cell skin cancers (discussed below), but it is far more dangerous. Like basal cell and squamous cell skin cancers, melanoma is almost always curable in its early stages. However, it is much more likely than basal or squamous cell cancers to spread to other parts of the body if not caught early.
Other Skin Cancers
Skin cancers that are not melanoma are sometimes grouped together as nonmelanoma skin cancers because they develop from skin cells other than melanocytes. They tend to behave very differently from melanomas and are often treated in different ways.
Nonmelanoma skin cancers include basal cell cancer and squamous cell cancer. Basal cell and squamous cell skin cancers are by far the most common skin cancers and are actually more common than any other form of cancer. Because they rarely metastasize (spread elsewhere in the body), basal cell and squamous cell skin cancers are less worrisome and are treated differently from melanomas. Merkel cell carcinoma is an uncommon type of skin cancer that is sometimes harder to treat.
For information about these and other types of nonmelanoma skin cancers, contact your American Cancer Society at 800-227-2345 and request the documents Skin Cancer — Basal and Squamous Cell, Kaposi Sarcoma, or Lymphoma of the Skin, or visit our Web site, cancer.org. Basal and squamous cell skin cancers are also discussed in the American Cancer Society book QuickFACTS Basal and Squamous Cell Skin Cancer.
What Are the Key Statistics About Melanoma?
Skin cancer is by far the most common of all cancers. Melanoma accounts for less than 5% of skin cancer cases but causes most skin cancer deaths.
The American Cancer Society estimates that about 70,230 new melanomas will be diagnosed in the United States during 2011 (about 40,010 in men; 30,220 in women). Incidence rates for melanoma have been increasing for at least 30 years. In recent years, the increases have been most pronounced in young white women and in older white men.
Melanoma is more than 10 times more common in whites than in blacks. It is slightly more common in men than in women. Overall, the lifetime risk of melanoma is about 2% (1 in 50) for whites, 0.1% (1 in 1,000) for blacks, and 0.5% (1 in 200) for Hispanics. The risk for each person can be affected by a number of different factors, which are described in the section "What Are the Risk Factors for Melanoma?"
Unlike many other common cancers, melanoma has a wide age distribution. It occurs in younger and older people. Rates increase with age and are highest among people in their 80s, but melanoma is not uncommon even among people younger than 30. It is one of the most common cancers in young adults.
About 8,790 people in the United States are expected to die of melanoma during 2011 (about 5,750 men and 3,040 women). The death rate has been dropping since the 1990s for people younger than 50 but has been stable or rising in people older than 50.
For information on survival rates for melanoma, see the section "How Is Melanoma Staged?"CHAPTER 2
Risk Factors and Causes
What Are the Risk Factors for Melanoma?
A risk factor is anything that affects your chance of having a disease such as cancer. Different types of cancer have different risk factors. For example, smoking is a risk factor for cancers of the lung, mouth, larynx (voice box), bladder, kidney, and several other organs.
Risk factors do not tell us everything, however. Having a risk factor, or even several risk factors, does not mean that you will get the disease. Melanoma develops in many people who do not have any known risk factors. Even if a person with melanoma has a risk factor, it can be difficult to know how much that risk factor may have contributed to the cancer.
Scientists have found several risk factors that may place you at higher risk for melanoma.
Exposure to Ultraviolet Radiation
Exposure to ultraviolet (UV) radiation is the main risk factor for most melanomas. Sunlight is the main source of UV radiation, which can damage the genes in your skin cells. Tanning lamps, beds, and booths are also sources of UV radiation. People with high levels of exposure to radiation from these sources are at greater risk for skin cancer, including melanoma.
Ultraviolet radiation is divided into 3 wavelength ranges:
UVA rays cause cells to age and can cause some damage to cells' DNA. They are linked to long-term skin damage such as wrinkles, but they are also thought to play a role in some skin cancers.
UVB rays can cause direct damage to the DNA, and they are the rays that primarily cause sunburns. They are also thought to cause most skin cancers.
UVC rays do not penetrate our atmosphere. They are not a cause of skin cancer.
Although UVA and UVB rays make up only a very small portion of the sun's wavelengths, they are the main cause of the sun's damaging effects on the skin. UV radiation damages the DNA of skin cells. Skin cancers begin when this damage affects the DNA of genes that control skin cell growth. Both UVA and UVB rays damage skin and cause skin cancer. UVB rays are a more potent cause of at least some skin cancers, but based on what is known today, there are no safe UV rays.
The amount of exposure to UV radiation depends on the intensity of the radiation, the length of time the skin was exposed, and whether the skin was protected with clothing and sunscreen.
The nature of the UV exposure may play a role in melanoma development. Many studies have linked the development of melanoma on the legs, arms, and trunk of the body to frequent sunburns, especially in childhood. The fact that these areas are not constantly exposed to UV radiation may also be important. Some experts think that melanomas in these areas are different from melanomas on the face and neck, where sun exposure is more constant. Melanomas that develop on areas where there has been little or no sun exposure, such as the palms of the hands, soles of the feet, underneath the nails, or internal surfaces such as the mouth and vagina, are different from either of the other types of melanoma.
For information on how to protect yourself and your family from UV exposure, see the section "Can Melanoma Be Prevented?" on page 19.
A nevus, or mole, is a benign melanocytic tumor. Moles are not usually present at birth, but they begin to appear in childhood. Most moles will never cause any problems, but a person who has many moles is at higher risk for melanoma.
A dysplastic nevus may look a little like a normal mole and a little like melanoma. They are often larger than other moles and have an abnormal shape or color. (See the section "Can Melanoma Be Found Early?" on pages 27–28 for descriptions of the appearance of moles and melanomas.) Dysplastic nevi can appear in areas that are exposed to the sun and in areas that are usually covered, such as the buttocks and scalp.
A small number of dysplastic nevi develop into melanomas, but most dysplastic nevi never become cancerous. Many melanomas seem to arise without a preexisting dysplastic nevus.
Lifetime melanoma risk may be higher than 10% for those with many dysplastic nevi, a condition sometimes referred to as dysplastic nevus syndrome. Dysplastic nevi often run in families. Lifetime risk goes up if the person also has close relatives who have had melanoma. A person with a large number of dysplastic nevi and several close relatives who have had melanoma has a 50% or greater lifetime risk of melanoma.
People with dysplastic nevus syndrome should have periodic thorough skin examinations performed by a dermatologist (a doctor who specializes in skin problems). In some cases, full body photographs are taken to help the doctor recognize which moles are changing and growing. Many doctors recommend that people be taught to do monthly skin self-examinations and be counseled about sun protection.
Congenital melanocytic nevi
Moles present at birth are called congenital melanocytic nevi. The lifetime risk of melanoma developing for people with congenital melanocytic nevi has been estimated to be between 0% and 10%, depending on the size of the nevus. People with very large congenital nevi have a greater risk, while the risk is smaller for those with small nevi.
Congenital nevi are sometimes removed by surgery so that they do not have a chance to become cancerous. The decision to remove a congenital nevus is influenced by several factors, including its size, location, and color. Many doctors recommend that congenital nevi be examined regularly by a dermatologist. People with congenital nevi should also be taught how to do monthly skin self-examinations.
The chance of any single mole turning into cancer is very low. However, anyone with lots of irregular or large moles has an increased risk of melanoma.
Fair Skin, Freckling, and Light Hair
The risk of melanoma is more than 10 times higher for whites than for blacks. This is because skin pigment has a protective effect. Whites with red or blond hair or fair skin that freckles or burns easily are at increased risk. Red-haired people have the highest risk.
Excerpted from Melanoma Skin Cancer by American Cancer Society. Copyright © 2012 American Cancer Society. Excerpted by permission of American Cancer Society / Health Promotions.
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