Actinic Keratosis (AK)

Epidemiology and Etiology:

•  >40y mostly
• fair complexed people who do not tan readily
• may develop in areas of vitiligo
• sunlight exposure is important

Common sites:

•  sun-exposed skin
• face
• ears
• scalp
• hands
• forearms

Gross features:

•  circumscribed
• scaly
• erythematous
• <1cm usually
• hypertrophic form:
• thick
• spreading pigmented AK:
• brown patch or plaque
• >1cm usually
• spreads centrifugally
• no mucin deposition in the papillary dermis
• no stromal retraction

Histologic features:

• loss of orderly stratified arrangement of the epidermis
• cytologic atypia of keratinocytes
• focal parakeratosis
• parakeratotic scale may form a cutaneous horn
• loss of underlying granular layer
• slightly thickened epidermis
• some irregular downward buds
• some cases the epidermis is thin (uncommon) 
• solar elastosis in the dermis, usually severe
• dilated vessels in the papillary dermis
• may see:
• suptrabasal cleft
• hyperplastic / hypertrophic form (superimposed lichen simplex chronicus)
• prominent orthokeratosis with alternating parakeratosis
• irregular psoriasiform hyperplasia
• mild papillomatosis sometimes

Immunophenotype:

Marker:	Sensitivity:	Specificity:
Ber-EP4 (neg)

Molecular features:

Other features:

• 8-20% progress to SCC if left untreated 

References: