What is Melanoma?
What Is Melanoma Skin Cancer?
Melanoma is a cancer that starts in a certain type of skin cell. To understand melanoma, it helps to know a little about the skin.
Normal skin
The skin is the largest organ in the body. It does many different things:
* Covers and protects the organs inside the body
* Helps to keep out germs
* Helps keep in water and other fluids
* Helps control body temperature
* Sends messages to the brain about heat, cold, touch, and pain
The skin has 3 layers. From the outside in, they are:
* Epidermis
* Dermis
* Subcutis
Diagram of the layers of the skin (Figure 1)
The top layer of the skin, the epidermis, is very thin and protects the deeper layers of skin and the organs. The epidermis itself has 3 layers. The bottom layer is made up of basal cells. These basal cells divide to form keratinocytes, which make a protein called keratin. This protein helps the skin protect the body.
The outermost part of the epidermis is called the stratum corneum, or horny layer. It is made of dead keratinocytes that are shed as new ones form. The cells in this layer are called squamous cells.
Another type of cell, the melanocyte, is also found in the epidermis. These cells make the brown pigment called melanin. Melanin makes skin tan or brown and protects the deeper layers of the skin from some of the harmful effects of the sun. Melanocytes are the cells that can become melanoma.
A layer called the basement membrane separates the epidermis from the deeper layers of skin. The basement membrane is important because when a cancer becomes more advanced it grows through this barrier.
Melanoma skin cancers
Melanoma is a cancer that begins in the melanocytes. Because most of these cells still make melanin, melanoma tumors are often brown or black. But this is not always the case, and melanomas can also have no color. Melanoma most often starts on the trunk (chest or back) in men and on the legs of women, but it can start in other places, too. Having dark skin lowers the risk of melanoma. But it does not mean that a person with dark skin will never get melanoma.
Melanoma can almost always be cured in its early stages. But it is likely to spread to other parts of the body if it is not caught early. Melanoma is much less common than basal cell and squamous cell skin cancers (described below), but it is far more dangerous.
Other skin cancers
Skin cancers that are not melanoma are sometimes grouped together as non-melanoma skin cancers because they start in skin cells other than melanocytes. These cancers include basal cell and squamous cell cancers. They are much more common than melanoma. Because they rarely spread, basal cell and squamous cell skin cancers are less worrisome and are treated differently than melanoma. They are discussed in our document called Skin Cancer: Basal and Squamous Cell.
Skin tumors that are not cancer
Most skin tumors are not cancer (they are benign). These rarely, if ever, turn into cancer. Some of them include:
* Seborrheic keratoses — tan, brown, or black raised spots with a “waxy” texture, or rough surface
* Hemangiomas — benign blood vessel growths often called strawberry spots or port wine stains
* Lipomas — soft growths of benign fat cells
* Warts — rough-surfaced growths caused by a virus
* Moles (also called nevi) — benign skin tumors that start from melanocytes
* Spitz nevus — a kind of skin tumor that sometimes looks a lot like melanoma
How Many People Get Melanoma Skin Cancer?
The American Cancer Society’s most recent estimates for melanoma in the United States are for 2009:
* 68,720 new cases of melanoma
* 8,650 deaths from melanoma
Skin cancer is the most common of all cancers. Melanoma accounts for less than 5% of skin cancer cases. But it causes most skin cancer deaths. The number of new cases of melanoma in the United States has been increasing for at least 30 years. Overall, the lifetime risk of getting melanoma is about 1 in 50 for whites, 1 in 1,000 for blacks, 1 in 200 for Hispanics.
What Causes Melanoma Skin Cancer?
We do not yet know exactly what causes melanoma skin cancer. But we do know that certain risk factors are linked to this disease. A risk factor is anything that affects your chance of getting a disease. Different cancers have different risk factors. Some risk factors, like smoking, can be controlled. Others, like a person’s age or family history, can’t be changed.
But risk factors don’t tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may not have any known risk factors. Even if a person with melanoma has a risk factor, it is often very hard to know how much that risk factor may have contributed to the cancer.