Seborrheic Keratosis
Epidemiology:
- Middle-aged and
older individuals
Common sites:
- Trunk
- Extremities, head,
neck
Gross features:
- Round
- “stuck on”
- flat plaques
- tan to dark brown
- velvety or
granular surface
- hand lens:
- small, round, porelike ostia impacted
with keratin
Histologic features:
- exophytic
- can draw a
straight line across bottom of epidermis from uninvolved skin through
lesion
- sharply demarcated
- sheets of basaloid cells
- exuberant
hyperkeratosis
- horn cysts
(characteristic)
- low mitotic activity
- no peripheral palisading
- squamous differentiation may be present (when
irritated or inflamed)
- may grow in an endophytic fashion when hair follicles involved
(inverted follicular keratosis)
Immunophenotype:
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Marker:
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Sensitivity:
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Specificity:
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Molecular features:
Other features:
- In dark-skinned individuals, multiple small lesions on
face occur – dermatosis papulosa
nigra
- Multiple SKs can be seen as a paraneoplastic
syndrome (Leser-Trelat sign)
- Transforming
growth factor alpha produced by neoplastic
cells
References: