Encyclopedia of Health and Medicine

skin cancer 197
structure or the SEBACEOUS GLAND (sometimes collectively
called the pilosebaceous unit). Basal cell
carcinomas nearly always arise on sun-exposed
skin surfaces, though may also occur on skin
exposed to radiation such as for RADIATION THERAPY.
The characteristic symptoms of basal cell carcinoma
are
• open sore that does not heal
• reddened or flaky patch that itches or hurts
• shiny, discolored NODULE (bump) that develops
on the skin
• pinkish, craterlike structure with raised edges
and tiny BLOOD vessels visible in the center
• yellowish, waxy area that resembles a scar
though gradually enlarges and may itch
Though basal cell carcinomas rarely metastasize,
they do spread within the epidermis and can
cause considerable damage to the skin. Doctors
diagnose about 800,000 Americans with basal cell
carcinoma each year, making it the most common
cancer of any type. A person who has one basal
cell carcinoma is likely to develop others, though
removed tumors seldom recur. Basal cell carcinoma
is uncommon in dark-skinned people.
Squamous Cell Carcinoma
Squamous cell carcinoma is a cancer of the keratinocytes
in the upper layer of the epidermis, formerly
called squamous cells because of their
squamous, or squashed, appearance. Nearly all
squamous cell carcinoma evolves from ACTINIC
KERATOSIS (though not all actinic keratosis lesions
become cancer). Because of this, doctors consider
actinic lesions precancerous and remove them to
end their progression, effectively thwarting the
cancer’s development. Squamous cell carcinoma
can but does not often metastasize. Sun damage
causes most squamous cell carcinoma, though
tumors can form in sites of continual irritation.
The characteristic symptoms of squamous cell
carcinoma are
• crusted, raised growth resembling a WART that
easily or frequently bleeds
• patch of red, flaky skin that oozes or bleeds
• sore that bleeds and crusts but does not go
away
• ulceration on the lips that resembles a COLD
SORE but does not heal
Though most commonly a cancer of the surface
skin (particularly sun-exposed), squamous cell
carcinoma also can develop in the mucous membranes.
Untreated squamous cell carcinoma will
eventually grow downward to penetrate the dermis
and subcutaneous layer, and may spread to
LYMPH structures that enable widespread metastasis.
Doctors diagnose about 200,000 Americans
with squamous cell carcinoma each year. Though
squamous cell carcinoma is less common in darkskinned
than in light-skinned people, among skin
cancers in dark-skinned people squamous cell carcinoma
is the most common.
Malignant Melanoma
Malignant melanoma arises from melanocytes, the
cells that produce melanin. Benign skin lesions
such as nevi (moles) composed of melanocytes are
often the staging sites for malignant melanoma.
Malignant melanoma can develop and metastasize
quickly. Diligent monitoring for changes in existing
lesions such as moles is the most effective
method for early detection and diagnosis. Doctors
classify malignant melanoma by growth pattern
(such as nodular, superficial, or spreading) or by
depth of invasion, metastasis, and nodal involvement.
Small, localized malignant melanomas are
about 90 percent curable with early diagnosis and
treatment. Widely metastasized malignant melanoma
is usually fatal.
The characteristic symptoms of malignant
melanoma are
• change in the size, symmetry, color, or texture
of an existing NEVUS (mole)
• bleeding or oozing from an existing nevus
• a new nevus that emerges and grows rapidly,
especially one that has asymmetrical shape,
irregular borders, multiple colors, or exceeds
one quarter inch in diameter (the ABCD criteria)
Doctors diagnose about 50,000 Americans with
malignant melanoma each year, many of whom
have moderate to advanced cancer by the time of
diagnosis.