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Dermatopathology
- About Skin Cancer
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Skin cancer begins in the
epidermis, or outer layer of skin. The epidermis
is very thin, averaging only 0.2 mm (about
one hundredth of an inch). It protects the
deeper layers of the skin and the organs of
the body from the environment. The epidermis
is made up of flat cells called squamous cells.
These cells form an important protein called
keratin, which contributes to the skin's ability
to protect the rest of the body.
Skin cancer is the most common type of cancer,
accounting for about half of all cancers.
Nonmelanoma (basal cell carcinoma or squamous
cell carcinoma) is more common than melanoma,
but melanoma is much more serious and more
likely to spread. According to the American
Cancer Society, melanoma accounts for about
four percent of skin cancer cases, but causes
about 79 percent of skin cancer deaths.
The three most common types of skin cancer
are melanoma, basal cell carcinoma and squamous
cell carcinoma. Basal cell carcinoma and squamous
cell carcinoma, along with several rare forms
of skin cancer, are referred to collectively
as nonmelanoma skin cancer.
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Melanoma
Melanoma skin cancer begins in the melanocytes, the
cells that produce the skin coloring or pigment known
as melanin. Other names for this cancer include malignant
melanoma, melanoma skin cancer and cutaneous melanoma.
Melanoma is much less common than nonmelanoma, but
it is much more serious and more likely to spread
to other parts of the body. Melanoma most often
appears on the trunk of fair-skinned men and on
the lower legs of fair-skinned women. However, people
with other skin types and other areas of the skin
are commonly affected. Because most melanoma cells
still produce melanin, melanoma tumors are often
brown or black. Although it is rare, melanomas can
form in parts of the body not covered by skin such
as the eyes, mouth, vagina, large intestine and
other internal organs.
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Non-Melanoma
Basal and squamous cell carcinomas are the most
common types of nonmelanoma skin cancer. They are
called nonmelanoma because they develop from skin
cells other than melanocytes. The two most common
types of nonmelanoma include:
Basal cell carcinoma - This is a
slow-growing cancer that seldom spreads to other
parts of the body. It looks like a pearly growth,
sometimes with an area that won't heal. It can be
translucent and grow gradually, or it can look like
a sore that won't heal.
Squamous cell carcinoma - This form
of nonmelanoma also rarely spreads, but it spreads
more often than basal cell carcinoma. It looks like
a crusty, scaly patch with a hard, callous-like
surface.
Other nonmelanoma skin cancers include Kaposi's
sarcoma, cutaneous lymphoma, skin adnexal tumors,
various types of sarcomas (cancers that develop
from connective tissue cells of the dermis or
subcutis), and Merkel cell carcinoma. Together,
these types account for less than one percent
of nonmelanoma skin cancers.
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Precancerous skin conditions
There are also some precancerous skin
conditions that can develop into skin cancer. These
include actinic keratosis and squamous cell carcinoma
in situ. Actinic keratosis--Actinic keratosis,
caused by overexposure to the sun, appears as rough
red or brown, scaly patches. Like skin cancer, it
usually appears on sun-exposed areas, but it can
be found anywhere on the body. It grows slowly and
usually does not cause any symptoms or signs other
than patches on the skin. It is possible, but not
common, for actinic keratoses to turn into squamous
cell cancer. Many times the patches go away, but
they may come back.
Squamous cell carcinoma in situ -- also called
Bowen's disease, is the earliest form of squamous
cell skin cancer. The cancer cells are only found
in the outer layer of skin and appear as reddish-colored
patches. Compared to actinic keratosis, the patches
of Bowen's disease tend to be larger (often over
1/2 inch wide), redder, more scaly and crusted.
Atypical moles (dysplastic nevi) are moles that
share many of the clinical features of melanoma.
Atypical moles occasionally develop into malignant
melanomas.
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