Melanoma is the most serious type of cancer affecting the skin. Each year in the United States, more than 53,600 people learn that they have it. In some parts of the world, especially among Western countries, it is becoming more common every year. In the United States, for example, the percentage of people who develop melanoma has more than doubled in the past 30 years.
Melanoma is one of the most serious types of
skin cancer because advanced melanomas have the ability to spread to other parts of the body. When melanoma starts in the skin, the disease is called cutaneous melanoma. It can also develop in the eye (called
intraocular melanoma) or in other parts of the body where pigment cells are found. In rare cases, it may arise in the meninges, the digestive tract, lymph nodes, or other areas where melanocytes are found. Melanomas that begin in areas other than the skin are not discussed in this article.
The skin is the body's largest organ. The skin:
- Protects against heat, sunlight, injury, and infection
- Helps control body temperature
- Stores water, fat, and vitamin D.
The skin has several layers, but the two main layers are the epidermis (the upper or outer layer) and the dermis (the lower or inner layer).
Skin cancer begins in the epidermis, which is made up of three kinds of cells:
- Squamous cells: Thin, flat cells that form the top layer of the epidermis.
- Basal cells: Round cells under the squamous cells.
- Melanocytes: Found in the lower part of the epidermis, these cells make melanin, the pigment that gives skin its natural color. When skin is exposed to the sun, melanocytes make more pigment, causing the skin to tan, or darken.
Understanding Melanocytes
Melanoma begins when melanocytes (pigment cells) gradually become more abnormal and divide without control or order. These cells can invade and destroy the normal cells around them. The abnormal cells form a growth of malignant tissue (a cancerous tumor) on the surface of the skin. Melanoma can begin either in an existing mole or as a new growth on the skin.
In men, melanoma is often found on the trunk (the area from the shoulders to the hips) or the head and neck. In women, melanoma often develops on the arms and legs. Melanoma usually occurs in adults, but is sometimes found in children and adolescents.
A doctor should be consulted if any of the following possible
melanoma symptoms occur. Symptoms of melanoma include a mole that:
- Changes in size, shape, or color
- Has irregular edges or borders
- Is more than one color
- Is asymmetrical (if the mole is divided in half, the two halves are different in size or shape
- Itches
- Changes in pigmented (colored) skin
- Develops satellite moles (new moles that grow near an existing mole)
- Oozes, bleeds, or is ulcerated (a hole forms in the skin when the top layer of cells breaks down and the underlying tissue shows through).
A doctor or nurse specialist can tell whether an abnormal-looking mole should be closely watched or should be removed and checked for melanoma cells. The purpose of routine
skin exams is to identify and follow abnormal moles. The removal of the entire mole or a sample of tissue for examination under a microscope is called a biopsy. If possible, it is best to remove moles by an excisional biopsy, rather than a shave biopsy.
If cancer cells are seen with the biopsy and a
melanoma diagnosis is made, the patient and the doctor should work together to make appropriate treatment decisions.
In many cases, melanoma can be cured by minimal surgery if the tumor is discovered when it is thin (before it has grown downward from the skin surface) and before the cancer cells have begun to spread to other places in the body. However, if it is not found early, the cancer cells can spread through the bloodstream and lymphatic system to form tumors in other parts of the body. Melanoma is much harder to control when it has spread. The spread of cancer is called metastasis.
At this time, no one can explain why one person will get melanoma and another person will not. Research has shown that sun exposure, especially excessive exposure that leads to bad, blistering sunburns, is an important and avoidable risk factor. Scientists are continuing their studies to find possible causes of this condition.
Risk Factors for Melanoma
Learning about
melanoma prevention and early detection is especially important for people who have an increased risk for developing the disease. People who are at an increased risk include those who have dysplastic nevi or a large number of ordinary moles.
Risk factors for melanoma include:
- Dysplastic nevi
- History of melanoma
- Family history of melanoma
- Weakened immune system
- Several ordinary moles (more than 50)
- Exposure to ultraviolet (UV) radiation
- Severe, blistering sunburns
- Freckles
- Fair skin.
It is important to remember that not everyone who has risk factors will get the disease. In fact, most do not. Also, about half the people who develop melanoma do not have any known risk factors for the condition.
Key points to keep in mind regarding melanoma include:
- It is a disease in which malignant (cancerous) cells form in the skin cells called melanocytes (cells that color the skin)
- It can occur anywhere on the body
- Unusual moles, exposure to sunlight, and health history can affect a person's risk of developing melanoma
- Possible signs of melanoma include a change in the appearance of a mole or pigmented area
- Tests that examine the skin are used to detect (find) and diagnose the disease
- Certain factors affect prognosis (chance of recovery) and treatment options for melanoma.
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