The Facts
Skin cancer is the most common type of cancer the United States.
About 1 million Americans develop skin cancer each year, and that number
is rising fast.
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 is less common than basal cell carcinoma, making
up about 20% of all non-melanoma skin cancers. It grows from the top layers
of skin, and is also found most often in sun-exposed areas.
Causes
Like melanoma, basal and squamous cell cancers are linked to sun exposure
early in life. Most people get the bulk of their 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 UV (ultraviolet light) skin damage.
In the United States, skin cancer is becoming more common in people under
40. The sunbathing responsible for today's skin tumors mostly happened 20,
30, or 40 years ago. In Australia, where people are exposed to a great deal of ultraviolet
light from an early age, skin cancer is a disease that strikes people in their
20s and 30s.
In the southern hemisphere, the changes in the ozone layer are far more dramatic
and are already affecting skin cancer rates. In Australia, where beach culture
has grown at the same time as the ozone has been depleted, skin cancer rates
have increased greatly.
People with fair skin, blonde or red hair, freckles, blue or green eyes, or
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 can cause a rare subtype of squamous
cell carcinoma.