Skin cancer is the most common type of cancer the United States. About 1 million Americans develop skin cancer each year, and that number continues to rise.
There are three types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma. This article deals with the first two types, which together are known as "non-melanoma skin cancer." Unlike melanoma, non-melanoma skin cancer has a low mortality rate and is often highly treatable. For information on melanoma, please see our melanoma article.
Basal cell carcinoma (BCC) is the most common skin cancer and is also the most common cancer. It grows from the basal (bottom) layer of the epidermis (the outer layer of the skin). It almost always appears on sun-exposed skin, such as the forehead, hands, lips, or tops of the earlobes. BCC makes up about 80% of all non-melanoma skin cancers. There are three main types of BCC:
- Superficial basal cell carcinoma (sBCC) often appears on the chest and upper body (torso) and possibly on the face. Commonly, it is a well-defined, scaly patch that looks similar to eczema. There is also often a thin, raised border that is pearl-colored around the affected patch of skin.
- Nodular BCC appears on areas exposed to the sun including the head and neck. It appears as an elevated bump of skin that is usually pearl-colored or pink.
- Morpheaform BCC appears as an ivory scar in areas that have never been injured or operated on. The tumor appears slightly raised and waxy, and is often white or yellowish in color. The borders of the tumor are not distinct.
There are also two more unusual types of BCC: pigmented BCC (similar to nodular BCC, but with black and brown pigmented areas) and cystic BCC (bluish-gray with a fluid-filled center).
Squamous cell carcinoma (SCC) is less common than basal cell carcinoma, but it is the second most common skin cancer. It grows from the top layers of skin, and is also found most often in sun-exposed areas.
Other types of non-melanoma skin cancer, such as Merkel cell carcinoma, Kaposi's sarcoma, or cutaneous T-cell lymphoma, are known as rare skin tumors and make up about 1% of non-melanoma skin cancers.
Like melanoma, basal and squamous cell cancers are linked to the sun. Most people get the majority of their lifetime sun exposure during childhood, and it's been shown that even one childhood sunburn increases the risk of developing skin cancer later in life. But a sunburn is not needed to damage the skin. A tan is also clear evidence of ultraviolet (UV) skin damage.
People with fair skin, blonde or red hair, freckles, blue or green eyes, or have difficulty tanning are at higher risk of skin cancer because they have less skin pigmentation and thus less protection from the sun.
Tumors generally grow when a normal cell suffers a mutation in its DNA, causing it to multiply without the usual restrictions. It's now believed that in basal cell carcinoma, a gene called PTC is damaged by UV radiation. This gene normally causes the cell to produce a protein that prevents runaway growth. A similar scenario may occur in squamous cell carcinoma.
Other causes of skin cancer include X-rays, skin contact with arsenic or radium, and possibly simple bad luck in that an error can occur spontaneously in a dividing cell despite low sun exposure. A sexually transmitted cancer-causing virus called the human papillomavirus (HPV) can cause a rare subtype of squamous cell carcinoma.