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U N I T 1 3
Integumentary Function
Skin Cancer
Skin cancer represents the most common malignancy
in white-skinned people in the Western world.
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The
majority of skin cancers are nonmelanomas, either
basal cell or squamous cell carcinoma, which are not
associated with a high risk of morbidity or mortality.
Although malignant melanoma represents a small subset
of skin cancers, it is the most deadly. In 2009 61,646
people in the United States were diagnosed with malig-
nant melanoma—35,436 men and 26,210 women.
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In
the United States, 9199 people also died from melano-
mas of the skin (5992 men and 3207 women).
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The
rising incidence of melanoma and other skin cancers has
been attributed to increased sun exposure associated
with social and lifestyle changes.
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The factors linking sun exposure to skin cancer are
not completely understood, but both total cumulative
exposure and altered patterns of exposure are strongly
implicated. Basal cell and squamous cell carcinomas are
often associated with total cumulative exposure to UV
radiation. Thus, basal cell and squamous cell carcinomas
occur more commonly on maximally sun-exposed parts
of the body, such as the face and back of the hands and
forearms. Melanomas occur most commonly on areas
of the body that are exposed to the sun intermittently,
such as the back in men and the lower legs in women.
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They are more common in persons with indoor occu-
pations whose exposure to sun is limited to weekends
and vacations. Excessive childhood sun exposure is an
important risk factor for melanoma, particularly blister-
ing sunburns.
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Malignant Melanoma
Malignant melanoma is a cancerous tumor of the mela-
nocytes.
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It is a rapidly progressing, metastatic form
of cancer. The dramatic increase in the incidence of
malignant melanoma over the past several decades has
been credited to increased UV light exposure, includ-
ing tanning salons. Other risk factors include a family
history of malignant melanoma, fair hair and skin, ten-
dency to freckle, and a history of blistering sunburns as
a child. Still other significant risk factors for melanoma
are atypical moles/dysplastic nevus syndrome, immuno-
suppression, and prior PUVA therapy.
Roughly 90% of malignant melanomas in whites
occur on sun-exposed skin. However, in darker-skinned
people melanomas often occur on non–sun-exposed
areas, such as the mucous membranes and subungual,
palmar, and plantar surfaces. Malignant melanomas dif-
fer in size and shape. Usually, they are slightly raised
and black or brown. Borders are irregular and surfaces
are uneven. Most appear to arise from preexisting nevi
or new molelike growths (Fig. 46-22). There may be
surrounding erythema, inflammation, and tenderness.
Periodically, melanomas ulcerate and bleed. Dark mela-
nomas are often mottled with shades of red, blue, and
white. These three colors represent three concurrent
processes: melanoma growth (blue), inflammation and
the body’s attempt to localize and destroy the tumor
(red), and scar tissue formation (white).
FIGURE 46-21.
Dysplastic nevi. Lesion has a dark brown
“pebbly” elevated surface against a lighter tan, macular
background.The irregular, indistinct margin helps to distinguish
it from the small congenital pattern nevus, which some
dysplastic nevi closely resemble. Its distinct morphology, rather
than its size (6 × 6 mm), identifies it as a dysplastic nevus (From
National Cancer Institute Visuals. No. AV-8500-3696.)
FIGURE 46-22.
Melanoma lesions, demonstrating the ABCD
rule: A (asymmetry), B (irregular borders), C (different colors),
and D (diameter change in size). (From National Cancer
Institute Visuals. Nos. AV-8809-4036, AV-8809-4037. Courtesy of
Skin Cancer Foundation.)
