Cancer starts when cells in a part of the body start to grow out of control. Cells in nearly any part of the body can become cancer. To learn more about how cancer starts and spreads, go to What Is 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.
The skin has 3 layers. From the outside in, they are:
- Epidermis: This top layer of the skin is very thin. The flat cells at the top of this layer are called squamous cells. Below this are cells called basal cells. Cells called melanocytes are also in the epidermis. These cells make the brown pigment melanin, which gives the skin its tan or brown color. Melanocytes are the cells that can become melanoma.
- Dermis: This middle layer of the skin is much thicker than the epidermis. It contains hair shafts, sweat glands, blood vessels, and nerves.
- Subcutis: This deepest layer of the skin contains proteins and fat, which help keep in body heat and act as a shock absorber to help protect the body’s organs from injury.
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:
- Mole (also called a nevus): a benign skin tumor that starts from melanocytes. Almost everyone has some moles. Nearly all of them are harmless, but some types can raise your risk of melanoma.
- Spitz nevus: a kind of mole that sometimes looks a lot like melanoma
- Seborrheic keratosis: a tan, brown, or black raised spot with a “waxy” texture
- Hemangioma: a benign blood vessel growth, often called a strawberry spot
- Lipoma: a soft growth made up of fat cells
- Wart: a rough-surfaced growth caused by some types of human papilloma virus (HPV)
Melanoma skin cancers
Melanoma is a cancer that begins in the melanocytes. Most of these cells still make melanin, so melanoma tumors are often brown or black. But melanomas can also appear pink, tan, or even white.
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 a person with dark skin can still 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.
Other skin cancers
Other types of skin cancers are sometimes grouped together as non-melanoma skin cancers.
Basal cell and squamous cell cancers are much more common than melanoma. Because they rarely spread to other parts of the body, these cancers are often less worrisome and are treated differently from melanoma. They are discussed in Skin Cancer: Basal and Squamous Cell.
Less common skin cancers
Other types of non-melanoma skin cancer are much less common than basal and squamous cell cancers and are treated differently. They include:
- Merkel cell carcinoma
- Kaposi sarcoma
- Skin lymphoma
- Skin adnexal tumors (tumors that start in hair follicles or skin glands)
- Various types of sarcomas
Together, these types account for less than 1% of all skin cancers.
Last Revised: 02/01/2016