Facts on File Encyclopedia of Health and Medicine

structure or the SEBACEOUS GLAND(sometimes col-
lectively 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 carci-
noma 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 BLOODvessels visible in the center


• yellowish, waxy area that resembles a scar
  though gradually enlarges and may itch

Though basal cell carcinomas rarely metasta-
size, 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 carci-
noma is uncommon in dark-skinned people.

Squamous Cell Carcinoma

Squamous cell carcinoma is a cancer of the ker-
atinocytes in the upper layer of the epidermis, for-
merly 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 WARTthat
  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
    SOREbut does not heal
  
  
  
  

Though most commonly a cancer of the surface

skin (particularly sun-exposed), squamous cell

carcinoma also can develop in the mucous mem-

branes. Untreated squamous cell carcinoma will

eventually grow downward to penetrate the der-

mis and subcutaneous layer, and may spread to

LY M P Hstructures that enable widespread metasta-

sis. Doctors diagnose about 200,000 Americans

with squamous cell carcinoma each year. Though

squamous cell carcinoma is less common in dark-

skinned than in light-skinned people, among skin

cancers in dark-skinned people squamous cell car-

cinoma 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 exist-

ing 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 involve-

ment. Small, localized malignant melanomas are

about 90 percent curable with early diagnosis and

treatment. Widely metastasized malignant mela-

noma 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 crite-
  ria)

Doctors diagnose about 50,000 Americans with

malignant melanoma each year, many of whom

have moderate to advanced cancer by the time of

diagnosis.

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