248
UNIT 3
Organ Systems
CLINICAL CORRELATION
Figure 13-5B.
Squamous Cell Carcinoma.
H&E,
3
108
Squamous cell carcinoma (SCC)
is the second most
common form of skin neoplasm. It originates from
keratinocytes of the epidermis. This carcinoma is
characterized by a slow-growing reddish or ulcerated
lesion with hard, raised borders. It is often found in
sun-exposed areas, with a high incidence in elderly
male Caucasians. Prolonged sun exposure, chronic
infl
ammatory lesions, and genetic factors, especially
p53 tumor suppressor gene mutations, contribute to
the development of the disease. SCCs called
actinic
keratoses
commonly arise in premalignant lesions on
sun-damaged skin. Carcinoma cells have enlarged and
hyperchromatic nuclei with variable differentiation,
some lesions producing abundant keratin. Treatment
includes surgical excision, cryosurgery, electrosurgery,
radiation therapy, and topical treatment.
Eosinophilic
squamous
cell carcinoma
cells
B
Figure 13-5A.
Stratum corneum of the epidermis, thin skin.
EM,
3
8,065; inset
3
21,889
The
stratum corneum
is the F nal product of the proliferation and differentiation that take place in the deeper layers of the epidermis. The
dead cells (
horny cells
) of the stratum corneum have lost the usual organelles and have become F lled with mature
keratin
, a tough net-
work of keratin intermediate F laments that are cross-linked by the protein F laggrin. Keratin and the persisting
desmosomes
between cells
account for the mechanical strength of the epidermis. Contributing to the relative impermeability of the stratum corneum is a coating of
involucrin linked to the inner surfaces of the plasma membrane and the presence of lipid that has been secreted into the spaces between
cells. In this specimen of thin skin, the
stratum granulosum
is only one cell thick, and some of its characteristic features (
keratohyalin gran-
ules
and
lamellar granules
) are not clearly discernible. Bundles of
tono± laments
,
melanin granules
, and
desmosomes
can be distinguished.
Remaining
Remaining
desmosomes
desmosomes
Remaining
desmosomes
Nucleus of stratum
spinosum cell
Cornified keratinocytes
Cornified envelope
Stratum granulosum
A
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